Thomas Aquinas Commentary Matthew 5:33-37

"Again, ye have heard that it was said to them of old time, Thou shalt not forswear thyself, but shalt perform unto the Lord thine oaths: but I say unto you, swear not at all; neither by the heaven, for it is the throne of God; nor by the earth, for it is the footstool of his feet; nor by Jerusalem, for it is the city of the great King. Neither shalt thou swear by thy head, for thou canst not make one hair white or black. But let your speech be, Yea, yea; Nay, nay: and whatsoever is more than these is of the evil [one]." — Matthew 5:33-37 (ASV)

Again you have heard that it was said to them of old, you shall not forswear yourself. Above, the Lord fulfilled one permissive precept, namely, concerning the bill of divorce. Here, He fulfills another permissive precept, namely, concerning oaths. And about this He does three things:

1. He cites the words of the Law;
2. He fulfills the precept; and
3. He answers a question.

The second part is where it is said, But I say to you not to swear at all; and the third part is where it is said, But let your speech be yea, yea: no, no.

Now it should be considered that two [kinds of moral precepts] are contained in the words of the Law, of which one was simply prohibitive, and the other permissive. There was a prohibitive precept regarding forswearing, namely, You have heard that it was said to them of old, you shall not forswear yourself, etc. You shall not swear falsely by my name, nor profane the name of your God. I am the Lord (Leviticus 19:12), and with almost the same meaning, You shall not take the name of the Lord your God in vain, etc. (Exodus 20:7). Regarding swearing, there was a permissive precept, namely, You shall perform your oaths to the Lord, meaning, when you have occasion to swear, you will not swear by creatures, but by God; as it is written, You shall fear the Lord your God, and shall serve him only, and you shall swear by his name (Deuteronomy 6:13). And according to this, it seems that this sacrament, namely, to swear by God, is not a sin, but that the Law permitted this because the Jews were prone to idolatry, not as though this thing were right, but so that something worse might be avoided, namely, idolatry.

But it remains, however, that to show reverence to God is good in itself. To swear by God is to show reverence to God, because everyone [swears by his god] and For men swear by one greater than themselves: and an oath for confirmation is the end of all their controversy (Hebrews 6:16). Therefore, to swear by God is good in itself. Furthermore, to swear by God is to invoke God as a witness. But this is good in itself. Therefore, to swear is good in itself.

And it should be known that in itself swearing is not something ordered; indeed, in itself it implies a disorder. To swear by God is nothing other than to invoke God as a witness to a human assertion; now this happens in two ways. It is either because the divine witness is adduced to confirm a human assertion, or because divine judgment is sought, as though it were said: ‘If it is not so, may the swearer be condemned by God.’ Among men’s deeds, however, nothing is so fragile as their words; If any man offend not in word, the same is a perfect man (James 3:2). Hence, to call upon God as a witness in these deeds in which man is so fragile is to despise God’s judgment; A man that sweareth much, shall be filled with iniquity .

The Lord, however, afterwards fulfills this precept here. Hence, He says, But I say to you not to swear at all, etc. Thus, an oath in itself is unlawful. Therefore, when judges compel men to swear in their lawsuits, it seems that they act contrary to this precept, and this is the opinion of certain heretics, saying that no one is allowed to swear. And Jerome replies that the Lord here forbids a man to swear by creatures, and He does this on account of the Jews, who were prone to idolatry. Hence, He does not simply forbid oaths. But this does not seem to be a good exposition, because then the Lord would have added nothing to the words of the Law, which says, You shall perform your oaths to the Lord.

And therefore, it should be said, according to Augustine, that the Lord forbids men to swear by God and by creatures.

But then there remains a twofold question. The first is that our Lord would have destroyed the Law, which says, You shall perform your oaths; and the second is that according to this, it seems that an oath would be unlawful. And Augustine replies that just as a bill of divorce was not intended by the Law, but was permitted on account of the cruelty of the Jews, and the Lord fulfilled it because He in no way wanted it to be given; similarly, here the Law commanded that they would not swear, but if they swore, they would swear not by creatures but by God; but the Lord fulfilled this when He said, Not to swear at all, etc. And just as he who is silent is in no way a liar, so he who in no way swears is further removed from perjury.

Regarding that which is said, namely, that an oath is unlawful, I answer, according to Augustine, that the same Holy Ghost is He who spoke in Sacred Scriptures and who also worked in the saints. Hence, what is the meaning of Scriptures appears in the sayings of the saints. Paul was moved by the Holy Ghost and yet he swore twice, for he swore with an oath of simple attestation: For God is my witness, whom I serve in my spirit in the gospel of his Son, that without ceasing I make a commemoration of you (Romans 1:9). And he swore with an oath of execration, which is when someone pledges their salvation or their soul to God: I call God to witness upon my soul that to spare you, I came not any more to Corinth (2 Corinthians 1:23).

And if it is said that this is not an oath, this is absurd, because to swear "by God" and "upon my soul" are the same; I die daily, I protest by your glory, brethren, which I have in Christ Jesus our Lord (1 Corinthians 15:31), and in Greek, the word "by" is so understood that one is swearing. Therefore, if Paul swore, it seems that the Lord did not intend to forbid swearing, but rather swearing easily. And Augustine shows that an oath is not something to be desired in itself, but on the contrary, only on account of the swearer's need. And therefore he says that Paul never swore except in writing, because it should not be done except with great caution and deliberation and on account of a need, that is to say, unless the good of others calls for it.

But someone could say that to swear by God is evil, but not by something less than God. And the Lord excludes this; hence, it is said, Neither by heaven for it is the throne of God, etc. To swear by creatures can be either from idolatry or without idolatry. For if judgment is attributed to those things, namely, by entreating judgment from creatures, then this is idolatry, just as the ancients did, who were saying that the heavens are a God. In another way, swearing by creatures can be without sin and idolatry in two ways. Firstly, insofar as a creature is pledged to God by entreating justice upon it, as for example, when men swear by their heads; secondly, insofar as in a creature there appears a reflection of the Divine Majesty, as for example, when an oath is sworn by heaven, whose power and potentiality is shown in the heavens. Hence, here He sets forth superior creatures by which someone might swear.

And this superiority is shown in three things, namely, in two elements, heaven and earth, and under which all other things are contained as means between extremes. And in regard to this, He says, Neither by heaven; Thus saith the Lord: Heaven is my throne, and the earth my footstool, etc. (Isaiah 66:1). Chrysostom says that He does not say, not to swear at all, neither by heaven because it is a great body, nor by the earth, which is the mother of all things, but He shows the excellence of these things in comparison with God.

But does God have limbs and posture and the like? Hence, this passage is expounded in two ways. Firstly, it is expounded literally. For that is called a seat where someone rests, and one rests where he abides perfectly. Therefore, because among corporeal creatures the heavens share the most in the divine goodness, and the earth the least, heaven is called God’s seat and earth His footstool. Likewise, men are accustomed to sit for judging, and because the Lord sometimes judges by means of those things which come from the heavens: And lighten with his light from above, he shall cover also the ends of the sea. For by these he judgeth people, and giveth food to many mortals (Job 36:30–31), namely, by means of lightning and the like, and so heaven is called His seat.

Mystically, however, by heaven, holy men are understood, whose conversation is in heaven: But our conversation is in heaven (Philippians 3:20). God judges in these men: But the spiritual man judgeth all things (1 Corinthians 2:15). By the earth, sinners are understood, on account of their affection for earthly things: They are enemies of the cross of Christ… who mind earthly things (Philippians 3:18–20). And [God’s feet are] upon this footstool, because if men do not fulfill the laws to which they are subject, they will be punished.

In human society men establish cities, and Jerusalem excels among other cities because God was worshipped there, and so these words are said, nor by Jerusalem; Glorious things are said of thee, O city of God (Psalms 86:3), and, Jerusalem, which is built as a city, which is compact together. For thither did the tribes go up, the tribes of the Lord: the testimony of Israel, to praise the name of the Lord (Psalms 121:3–4).

And then the Lord speaks concerning bodily members. But since it could be said that we should not swear by these greater things, but by lesser things, He says, Neither shall you swear by your head. For anyone can do what he wishes with that which is his, but man does not have power over his head as to smallest matters. Therefore, one should not swear by that member and this is what is said, because you cannot make one hair white or black, naturally speaking, namely, And which of you by taking thought, can add to his stature one cubit? (Matthew 6:27).

But it could be said: How then will we speak? He replies, and in this He does two things:

1. He answers the question; and
2. He gives the reason.

He says, therefore, But let your speech be yea, yea: no, no. And it can be expounded in three ways.

1. If someone were to ask, ‘Is it so?’ let your speech be yea, yea: no, no.
2. It is expounded as follows: Let not your mouth say one thing, and your heart feel another thing, and your deed show yet another thing. With the workers of iniquity destroy me not: Who speak peace with their neighbor, but evils are in their hearts (Psalms 27:3).
3. It is expounded as follows, and it is more literal: Let your speech be yea, yea: no, no, as though He were to say: ‘May you say both simply.’ For this is the definition of truth, namely, everything that is, is said to be; and what is not, is said not to be. This is Hilary’s exposition: For the Son of God, Jesus Christ… was not: It is and It is not. But, It is, was in him (2 Corinthians 1:19).

And that which is over and above these, is of evil. He does not say, ‘is evil,’ but, ‘is of evil,’ and it is not from your evil but from another’s evil, because you are forced to swear, although nevertheless it would be beneficial for him to believe your oath; and the Apostle swore in this way. Or it is expounded, according to Chrysostom, as follows: And that which is over and above these, is of evil. By this it appears that in the Old Law one oath was prohibitive, namely, to perjure; it permitted another, namely, to swear out of necessity; it rejected a third oath, namely, a superstitious oath, which is when reverence is shown to a creature which is owed to God.