Thomas Aquinas Commentary Galatians 3:15-18

"Brethren, I speak after the manner of men: Though it be but a man`s covenant, yet when it hath been confirmed, no one maketh it void, or addeth thereto. Now to Abraham were the promises spoken, and to his seed. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ. Now this I say: A covenant confirmed beforehand by God, the law, which came four hundred and thirty years after, doth not disannul, so as to make the promise of none effect. For if the inheritance is of the law, it is no more of promise: but God hath granted it to Abraham by promise." — Galatians 3:15-18 (ASV)

Having proved by scriptural authority that the Law does not justify and is not necessary for justification, which is through faith, the Apostle then proves the same point with human reasoning. In this regard, he does four things:

1. He mentions a human custom.
2. He touches on a divine promise (verse 16).
3. He draws his conclusion (verse 17).
4. He shows that the conclusion follows from the premises (verse 18).

He says, therefore: It is clear that until now I have been speaking according to the authority of Sacred Scripture, which did not come by the will of man, but by the Holy Spirit, as is said in 2 Peter 1:21. But now I speak in a human way, according to the customs that human reason and tradition follow. Here, indeed, we have an argument showing that in discussions concerning faith, we may use any truth from any field of knowledge.

For example, “If you see in the number of the captives a beautiful woman and love her and will have her as your wife, you shall bring her into your house.” That is, if you are pleased with worldly wisdom and knowledge, bring it within your boundaries. “And she shall shave her hair and pare her nails”—that is, you must cut away all its erroneous opinions (Deuteronomy 21:11–12). This is why the Apostle uses the authority of the Gentiles in many places in his epistles, for example: “Evil communications corrupt good manners” (1 Corinthians 15:33), and “The Cretans are always liars, evil beasts, lazy gluttons” (Titus 1:12).

Alternatively, although such human reasoning may be fruitless and weak—because, as is said in Psalm 94:11, “The Lord knows the thoughts of men, that they are vain”—yet if a person’s testament is confirmed, no one disregards or adds to it. Nothing human has as much power to bind as a person’s last will. Someone would be scorning it if they were to say that a person’s will, confirmed by their death and by witnesses, had no validity.

Therefore, if no one scorns a human testament by saying it should not be heeded or by modifying it, much less may anyone scorn the testament of God, or modify and weaken it by adding or removing anything. As it is written: “If anyone adds to these things, God will add to him the plagues written in this book; and if anyone takes away from the words of the book of this prophecy, God will take away his part from the book of life” (Revelation 22:18–19). And also, “You shall not add to the word that I speak to you, nor shall you take away from it” (Deuteronomy 4:2).

Then, when he says, To Abraham and his seed were the promises made, he takes up the promise God made to Abraham, which is, as it were, the testament of God. In this, he does two things:

1. He explains this promise or testament.
2. He discloses the truth contained within it (verse 16), noting that Scripture does not say, “And to his seeds.”

He says, therefore: To Abraham and his seed were the promises made. It is as if to say: Just as a person’s testament is valid, so are the divine promises. But did God make any promises before the Law? He did. The promises were spoken—that is, made—by God to Abraham, who lived before the time of the Law, and to his seed. They were made to Abraham as the one for whom they would be fulfilled, and to his seed as the one through whom they would be fulfilled.

The Apostle says “promises,” using the plural, because the promise that his seed would be blessed contained a number of things, or because the same thing—namely, eternal happiness—was promised to him on a number of occasions. For example: “In you all the families of the earth shall be blessed” (Genesis 12:3); “Look up to heaven and number the stars, if you can. So shall your seed be” (Genesis 15:5); “To your seed I will give this land” (Genesis 15:18); and, “I will bless you, and I will multiply your seed as the stars of heaven” (Genesis 22:17). These promises, then, are God’s testament, so to speak—that is, a decree concerning the inheritance to be given to Abraham and his seed.

He explains the meaning of this testament when he says that Scripture does not say, “And to seeds,” as of many, but as of one, “And to your seed.” He explains this according to the very spirit in which the testament was made. This is clear from the words of the testament: it does not say, “and to his seeds,” as referring to many (that is, as it would if the promise were valid for many), but as referring to one: “And to your seed,” which is Christ. He is the only one through whom and in whom all could be blessed.

For Christ alone is the one who does not lie under the curse of guilt, even though He deigned to be made a curse for us. Hence it is said, “I am alone until I pass” (Psalms 141:10); and again, “There is none that does good, no, not one” (Psalms 14:3). It is also written, “One man among a thousand I have found” (namely, Christ, who was without any sin), “but a woman among all those I have not found” (Ecclesiastes 7:28)—that is, one who would be entirely immune from all sin, whether original or venial.

Then, with the words, Now this I say, he draws his conclusion. Let us examine in order what he says. He states that what God promised to Abraham is a testament—that is, a promise that he would obtain an inheritance: “I will make a new covenant with the house of Israel and with the house of Judah” (Jeremiah 31:31). He says it was confirmed by God (that is, by the One who promised), in keeping with what he said above: if a person’s testament is confirmed, no one disregards or adds to it. The testament was confirmed with an oath: “By myself I have sworn” (Genesis 22:16); “that by two unchangeable things, in which it is impossible for God to lie, we might have strong comfort” (Hebrews 6:18).

This testament, I say, the Law does not annul. The Law, which was made and given by God through Moses 430 years later (“For the law was given through Moses,”John 1:17), does not annul the testament so as to make the promise of no effect. The aforementioned testament would have been annulled if the promise made to Abraham were set aside—that is, made fruitless—as though the promised seed were not enough to bless the Gentiles.

As a matter of fact, the promises made to the patriarchs were not set aside by Christ but confirmed: “For I say that Christ Jesus was a minister of the circumcision to confirm the promises made to the fathers” (Romans 15:8); “For all the promises of God in him are ‘Yes’” (2 Corinthians 1:20). The 430 years agrees with Exodus 12:40 (“The time that the people of Israel lived in Egypt was 430 years”) and with Acts 7:6 (“And God said to him,” that is, to Abraham, “that his offspring would sojourn in a foreign land, and that they would be enslaved and afflicted for 430 years”).

Against this, however, it is said in Genesis 15:13: “Know for certain that your offspring will be sojourners in a land that is not theirs and will be servants there, and they will be afflicted for 400 years.”

I answer that if you count the years from the first promise made to Abraham (Genesis 12) to the exodus of the children of Israel from Egypt (when the Law was given), there are 430 years, as is written here and in Exodus 12 and Acts 7. But if you begin to count from the birth of Isaac (Genesis 21), there are only 405 years. This is because 25 years elapsed between the promise and Isaac’s birth: Abraham was 75 when the promise was made and 100 when Isaac was born.

The 405 years from Isaac’s birth to the exodus can be demonstrated. Isaac was 60 years old when he fathered Jacob (Genesis 25). Jacob was 130 years old when he entered Egypt (Genesis 47). Therefore, 190 years passed from the birth of Isaac to Jacob’s entry into Egypt. The Israelites then remained in Egypt for 215 years. This number is reached by adding the 71 years remaining in Joseph’s life after Jacob’s arrival to the 144 years the Israelites remained in Egypt after Joseph’s death, as Rabanus says in a gloss on Acts 7. Thus, 190 years plus 215 years equals 405 years.

The scripture in Genesis 15, therefore, was not concerned with such precise details and used the round number of 400. Alternatively, it can be said that in Isaac’s fifth year, Ishmael was cast out, leaving Isaac as the sole heir. Reckoning from that date, we arrive at exactly 400 years (405 - 5 = 400).

Then, when he says, For if the inheritance is by the law, it is no longer by promise, he shows how it follows from the previous points that the Law would nullify the promises if it were necessary for justification or for the blessing to come to the Gentiles. He says, therefore: The promise would indeed be annulled if the Law were necessary. For if the inheritance (namely, of Abraham’s blessing) is from the law, it is no longer from the promise (that is, from the seed promised to Abraham). If the promised seed was enough to obtain the inheritance of the blessing, then justification would not be through the Law. He rejects this consequence when he says, But God gave it to Abraham by a promise. This means God promised to give it, and the promise was as sure as if it had been fulfilled then and there. It was given by promise—that is, through the promised seed. Therefore, the inheritance—the blessing about which it is said, “For to this you were called, that you may obtain a blessing” (1 Peter 3:9)—is not from the Law.