Today, on this eighth and last day of the Week of Prayer for Christian Unity, we will look at what St. Thomas Aquinas says about the unity of the Church. Here I’ll offer some very brief remarks on what St. Thomas teaches concerning the unity of the Church. I’ll draw from Aquinas’ commentary on the Apostles’ Creed in his catechism, his Summa Contra Gentiles and his Summa Theologiae.

St Peter Martyr Altarpiece
Fra Angelico
1427-28
Museo di San Marco, Florence

The Aquinas Catechism

In the last year of his life, St. Thomas Aquinas preached a series of sermons during Lent in the city of Naples. According to a contemporary, almost the whole population of the city came daily to hear these sermons. Reginald de Piperno made careful transcripts of these sermons, which were aimed at providing a summary of the faith. In them, St. Thomas preached through the Apostle’s Creed, the Lord’s Prayer, the Ten Commandments, and the Sacraments.

In his comments on the line of the Apostles’ Creed “the holy catholic Church,” St. Thomas briefly talks about the four marks of the Church (i.e. one, holy, catholic and apostolic) explicitly taught in the Nicene Creed. One of those four marks is unity. Regarding the unity of the Church, St. Thomas first says the following:

The unity of the Church

Of the first, it must be known that the Church is one. Although various heretics have founded various sects, they do not belong to the Church, since they are but so many divisions whereas the Church is one. Of her it is said: “One is My dove; My perfect one is but one.” (Song of Solomon 6:8)

Various heretics have founded sects, St. Thomas says, but these sects do not belong to the Church. They may very well have been founded by well-intentioned persons; perhaps none of these founders of sects thought they were heretics, or that they were making a schism. But, says St. Thomas, these sects do not belong to the Church. They were founded by mere men. The Church, by contrast, was founded by the incarnate God-man, Jesus Christ. Only by remaining in the Church Christ founded do we truly participate in the supernatural unity Christ imparted to His Church. The sects show that they are not united, by their many divisions. The Church, by contrast, cannot be divided; unity is one of the four essential marks of the Church, because the Church’s unity is Christ’s unity, and Christ cannot be divided. (1 Cor 1:13) Schismatics and dissenters can separate themselves from her in various ways, but they cannot divide her.

St. Thomas goes on to show the three-fold sources of unity in the Church, in the three theological virtues of faith, hope, and charity. He says:

The unity of the Church arises from three sources:

(1) From the unity of faith. All Christians who are of the body of the Church believe the same doctrine. “I beseech you . . . that you all speak the same thing and that there be no schisms among you.” (1 Cor 1:10) And: “One Lord, one faith, one baptism;” (Eph 4:5)

(2) From the unity of hope. All are strengthened in one hope of arriving at eternal life. Hence, the Apostle says: “One body and one Spirit, as you are called in one hope of your calling;” (Eph 4:4)

(3) From the unity of charity. All are joined together in the love of God, and to each other in mutual love: “And the glory which Thou hast given Me, I have given them; that they may be one, as We also are one.” (John 17:22) It is clear that this is a true love when the members are solicitous for one another and sympathetic towards each other: “We may in all things grow up in Him who is the head, Christ. From whom the whole body, being compacted, and fitly joined together, by what every joint supplieth, according to the operation in the measure of every part, maketh increase of the body unto the edifying of itself in charity.” (Eph 4:15,16) This is because each one ought to make use of the grace God grants him, and be of service to his neighbor.

No one ought to be indifferent to the Church, or allow himself to be cut off and expelled from it; for there is but one Church in which men are saved, just as outside of the ark of Noah no one could be saved.

This is the unity of the Body of Christ. First that we share the same faith, i.e. the same doctrine, and the same sacraments. We also share the same hope, i.e. the hope of eternal life, not merely everlasting existence, but a glorious union with God in which we enjoy the Beatific Vision and thus enter into His eternal life of perfect beatitude. Finally, we are joined together in the supernatural virtue called ‘charity’ (i.e. agape), by which we freely give ourselves in joyful sacrifice to Christ, serving each other for His sake, all working together to build up His Body, the Church. Persons in schisms or sects are not all working to build up the same Body. They work to build up their own schism or sect, even seeking to snatch away members from the true Body. This opposition is evidence that the persons involved are not all members of the same Body.

Summa Contra Gentiles

In Chapter 76 of Book IV of his Summa Contra Gentiles, St. Thomas gives further insight into the nature of the unity of the Church. First he explains why bishops are necessary to administer the Sacrament of Order, also called Holy Orders. He writes:

There must be some power of higher ministry in the Church to administer the Sacrament of Order; and this is the episcopal power, which, though not exceeding the power of the simple priest in the consecration of the Body of Christ, exceeds it in its dealings with the faithful. The presbyter’s power is derived from the episcopal; and whenever any action, rising above what is common and usual, has to be done upon the faithful people, that is reserved to bishops; and it is by episcopal authority that presbyters do what is committed to them; and in their ministry they make use of things consecrated by bishops, as in the Eucharist the chalice, altar-stone and palls.

St. Thomas is saying here that with respect to the power to consecrate the Eucharist, the bishop has no greater power than does the priest. However, the presbyter’s (i.e. priest’s) power to consecrate the Eucharist is derived from the bishop’s power. It is by the bishop’s power, says St. Thomas, that presbyters “do what is committed to them.” They receive their power from the bishops; they also receive their commission from the bishops, and the sacred vessels they use have been consecrated by the bishops.

St. Thomas then gives three reasons why Christ established the Church to have one visible head. He writes:

1. Though populations are different in different dioceses and cities, still, as there is one Church, there must be one Christian people. As then in the spiritual people of one Church there is required one Bishop, who is Head of all that people; so in the whole Christian people it is requisite that there be one Head of the whole Church.

St. Thomas shows here that the requirement of one person as the visible head is a principle at every level of a society. Even though the universal Church is spread out all over the world, yet it is one society by the same principle of visible unity we find at every more particular level. Every parish has a priest, and if there is more than one priest, the other priests are his assistants. They do not all have equal authority, because that would lead to strife, conflict and division. Likewise, every diocese has a bishop who has charge over the priests in his diocese. If there is more than one bishop in a diocese, the others are auxillary bishops there to assist and serve the diocesan bishop, so that there is no cause for faction between them. Then St. Thomas points out that this need for a visible head at these local levels is no less present at the universal level. Just as the local Church requires a visible head, so the universal (i.e. catholic Church) requires a visible head. This visible head of the catholic Church supports and maintains the unity of the universal Church spread out throughout the whole world.

St. Thomas next provides a second reason:

2. One requisite of the unity of the Church is the agreement of all the faithful in faith. When questions of faith arise, the Church would be rent by diversity of judgments, were it not preserved in unity by the judgment of one. But in things necessary Christ is not wanting to His Church, which He has loved, and has shed His blood for it: since even of the Synagogue the Lord says: What is there that I ought further to have done for my vineyard and have not done it.? (Isai. v, 4.) We cannot doubt then that by the ordinance of Christ one man presides over the whole Church.

Here St. Thomas makes the following argument. The unity of the Church requires unity of faith (i.e. doctrine and sacraments). But when disputes about the faith arise, the Church would be torn apart into many schisms if there were not ultimately one person having the authority to adjudicate these disputes. Hence it is necessary for preserving the unity of the faith that there be one person presiding in the Church, having the authority to resolve such disputes. But Christ would not leave His Church without anything that is necessary for her preservation, since He has already shown that He is willing to shed all His blood for His Church. Therefore since such an office is necessary for the Church, and Christ would not fail to provide her with what is necessary, we cannot doubt that it is by Christ’s ordination that one man presides over the whole Church.

Lastly, St. Thomas provides a third reason:

3. None can doubt that the government of the Church is excellently well arranged, arranged as it is by Him through whom kings reign and lawgivers enact just things (Prov. viii, 15). But the best form of government for a multitude is to be governed by one: for the end of government is the peace and unity of its subjects: and one man is a more apt source of unity than many together.

The best form of government for a multitude is to governed by one. That is because the purpose of government is the peace and unity of the citizens governed. One man is better able to provide a unified course of direction than many leaders all with equal authority. This is why each country has one person as its governor at any given time, even if there are other governing bodies assisting and collaborating the individual leader. We all recognize the need for a unified head of government. This principle is no less true in the Church. The same God who ordered and arranged the natural requirements of governing cities and nations, is the same God who established and ordered His Church. St. Thomas is here implicitly making use of the principle that grace builds on nature. Just as the best form of government in the natural order requires a single visible head, so because grace builds on nature, the best form of government in the order of grace (i.e. the Church) likewise requires a single visible head. It would be arbitrary to acknowledge that a unified visible head is necessary at every level of the Church particular, but deny that a unified visible head is necessary at the level of the Church universal.

St. Thomas then anticipates and responds to two rather common Protestant objections, first, that the head of the universal Church is only Christ, and not a man whom Christ has appointed. He writes:

But if any will have it that the one Head and one Shepherd is Christ, as being the one Spouse of the one Church, his view is inadequate to the facts. For though clearly Christ Himself gives effect to the Sacraments of the Church, — He it is who baptizes, He forgives sins, He is the true Priest who has offered Himself on the altar of the cross, and by His power His Body is daily consecrated at our altars, — nevertheless, because He was not to be present in bodily shape with all His faithful, He chose ministers and would dispense His gifts to His faithful people through their hands. And by reason of the same future absence it was needful for Him to issue His commission to some one to take care of this universal Church in His stead. Hence He said to Peter before His Ascension, Feed my sheep (John xxi, 1) and before His Passion, Thou in thy turn confirm thy brethren (Luke xxii, 32); and to him alone He made the promise, To thee I will give the keys of the kingdom of heaven (Matt. xvi, 19).

St. Thomas shows that even though Christ is present in the sacraments of the Church, this sacramental presence is not adequate for the visible governance of the universal Church (as it is not adequate for visible governance of the local parish or diocese). This is why Christ set aside St. Peter, entrusted to him the keys of the Kingdom, and commissioned him to feed Christ’s sheep and strengthen his brethren. Because Christ, after His ascension is invisible in heaven, and because His sacramental presence is inadequate for the role of visible governance of the universal Church, therefore it was necessary that Christ choose one man to stand in His place as visible head of the universal Church, until His return.

St. Thomas then anticipates and responds to a second Protestant objection:

Nor can it be said that although He gave this dignity to Peter, it does not pass from Peter to others. For Christ instituted His Church to last to the end of the world, according to the text: He shall sit upon the throne of David and in his kingdom, to confirm and strengthen it in justice and judgment from henceforth, now, and for ever (Isai. ix, 7). Therefore, in constituting His ministers for the time, He intended their power to pass to posterity for the benefit of His Church to the end of the world, as He Himself says: Lo, I am with you to the end of the world (Matt. xxviii, 20).

The second objection is that the unique authority that Christ gave to St. Peter to be visible head of the universal Church, passed away with the death of St. Peter, and did not pass on to others who succeeded him. St. Thomas refutes that objection by showing that the need for such authority did not cease with the death of St. Peter, because Christ established His Church to endure until the end of the world.  Therefore Christ, knowing that the Church would continue long after the death of St. Peter, intended that the power He entrusted to St. Peter would pass on to his successors, “for the benefit of the Church to the end of the world.”

St. Thomas concludes:

Hereby is cast out the presumptuous error of some, who endeavour to withdraw themselves from obedience and subjection to Peter, not recognizing his successor, the Roman Pontiff, for the pastor of the Universal Church.

To reject obedience and subjection to St. Peter (and his successors) is to reject those persons who, by His authorization stand in His place, to govern His universal Church until He returns. Once a person recognizes that Christ entrusted this authority over the universal Church to St. Peter and his successors, he understands that to listen to St. Peter and his successors is to listen to Christ, and to reject St. Peter and his successors is to reject Christ.¹

Summa Theologiae

In St. Thomas’ Summa Theologiae we read the following:

Wherever there are several authorities directed to one purpose, there must needs be one universal authority over the particular authorities, because in all virtues and acts the order is according to the order of their ends (Ethic. i, 1,2). Now the common good is more Godlike than the particular good. Wherefore above the governing power which aims at a particular good there must be a universal governing power in respect of the common good, otherwise there would be no cohesion towards the one object. Hence since the whole Church is one body, it behooves, if this oneness is to be preserved, that there be a governing power in respect of the whole Church, above the episcopal power whereby each particular Church is governed, and this is the power of the Pope. Consequently those who deny this power are called schismatics as causing a division in the unity of the Church. Again, between a simple bishop and the Pope there are other degrees of rank corresponding to the degrees of union, in respect of which one congregation or community includes another; thus the community of a province includes the community of a city, and the community of a kingdom includes the community of one province, and the community of the whole world includes the community of one kingdom.²

The argument here is similar to what we saw in the Summa Contra Gentiles. The first point has to do with acts ordered to a single end. Whenever there are multiple authorities directed to one purpose, there must be a universal authority over these particular authorities, to order their acts toward one single end. Otherwise each authority will not be acting in unison with the other authorities. This is why armies have generals, and why there must be a commander-in-chief. If there is not a single unified leader of the army, then its various units will not be coordinated together to act in concer in one unified purpose and plan. Likewise, if there were not a visible governing authority for the universal Church, then the bishops of the various dioceses would likewise not be ordered in their actions toward one end in the visible Church. They would each be doing their own activity, according to their own plan and vision. But their actions would not be ordered toward one end, and so the universal Church would reduce to a collection of particular Churches. Just as without a commander-in-chief there would not be one army but as many armies as highest-ranking generals, so without a visible authority over the universal Church, there would not be one universal Church, but as many particular Churches as there are bishops.

According to St. Thomas, to deny the “power of the Pope,” is to make oneself a schismatic, by causing a division in the unity of the Church. The Church itself does not lose unity when a schism occurs; her unity is Christ’s unity. Rather, when a schism occurs, the Church loses the participation in her unity by the schismatic who separates himself from the authority of the Pope.

One other place in Aquinas’ Summa Theologiae is notable for its implications regarding the unity of the Church. That is the section on the sin of schism. In Summa Theologiae II-II Q.39 a.1, St. Thomas writes:

As Isidore says (Etym. viii, 3), schism takes its name “from being a scission of minds,” and scission is opposed to unity. Wherefore the sin of schism is one that is directly and essentially opposed to unity. For in the moral, as in the physical order, the species is not constituted by that which is accidental. Now, in the moral order, the essential is that which is intended, and that which results beside the intention, is, as it were, accidental. Hence the sin of schism is, properly speaking, a special sin, for the reason that the schismatic intends to sever himself from that unity which is the effect of charity: because charity unites not only one person to another with the bond of spiritual love, but also the whole Church in unity of spirit.

Accordingly schismatics properly so called are those who, willfully and intentionally separate themselves from the unity of the Church; for this is the chief unity, and the particular unity of several individuals among themselves is subordinate to the unity of the Church, even as the mutual adaptation of each member of a natural body is subordinate to the unity of the whole body. Now the unity of the Church consists in two things; namely, in the mutual connection or communion of the members of the Church, and again in the subordination of all the members of the Church to the one head, according to Colossians 2:18-19: “Puffed up by the sense of his flesh, and not holding the Head, from which the whole body, by joints and bands, being supplied with nourishment and compacted, groweth unto the increase of God.” Now this Head is Christ Himself, Whose viceregent in the Church is the Sovereign Pontiff. Wherefore schismatics are those who refuse to submit to the Sovereign Pontiff, and to hold communion with those members of the Church who acknowledge his supremacy.

We can learn something about the unity of the Church by studying the sin against that unity. Strictly speaking, says St. Thomas, the sin of schism is one in which the person willfully and intentionally separates himself from the unity of the Church.³ The person who does so in ignorance or unintentionally, is less culpable (if culpable). But the person who discovers himself to be in schism, even if born into that schism, is culpable if he does not seek to cease to be in schism. To willfully remove oneself from the unity of the Church, or to willfully remain in schism from the Church, is to sin against charity. As heresy is a sin against faith, so schism is a sin against the charity which “unites the whole Church in unity of spirit.”

What does it mean to be in schism? Some Christians think that so long as they love other Christians, they are therefore not in schism. But St. Thomas explains that the unity of the Church consists in two things: the mutual connection of the members of the Church, and the subordination of all the members to the Church’s visible head, who represents Christ. So there are two ways to be a schismatic, according to St. Thomas. One way is to refuse to hold communion with other members of the Church. The other way is to refuse to submit to the Sovereign Pontiff. Both forms of schism are sins against charity, for they both act against the charity by which the whole Church is held together in love.

Here we see the relation between authority and charity, described earlier this week in Jeremy Tate’s essay. Love and authority are not mutually exclusive. Rather, love for Christ is expressed by humbly subordinating ourselves to those with His authorization, especially the successor of the Apostle to whom Christ entrusted the keys of the Kingdom.

1. cf. Luke 10:16 [↩]
2. Summa Theologiae Supp. Q.40 a.6 [↩]
3. Here we see an implicit distinction between formal schism (intentional, willful schism), and material schism, i.e. schism that is unintentional or done in ignorance. [↩]