Thomas Aquinas, on Gal 3:15

“Brethren (I speak after the manner of man,) yet a man’s testament, if it be confirmed, no man despiseth, nor addeth to it.”

“Having proved by 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 reasons. Concerning this he does four things: First, he mentions a human custom; Secondly, he touches on a divine promise (v. 16); Thirdly, he draws his conclusion (v. 17); Fourthly, he shows that the conclusion follows from the premises (v. 18). He says therefore: It is clear that up to now I have been speaking according to the authority of Sacred Scripture, which came not by the will of man, but by the Holy Spirit, as is said in 2 Peter (1:21). But now "I speak after the manner of man" and after the manners which human reason and human custom follow. Here, indeed, we have an argument to show that in discussions bearing on faith, we may use any truth of any science: "If thou seest in the number of the captives a beautiful woman and lovest her and wilt have her to wife, thou shalt bring her into thy house," i.e., if you are pleased with worldly wisdom and science, bring it within your boundaries, "and she shall shave her hair, and pare her nails," i.e., you shall cut away all erroneous opinions (Deut 21:11). This is why in many places in his epistles the Apostle uses the authority of the Gentiles; for example: "Evil communications corrupt good manners" (1 Cor 15:33), and "The Cretans are always liars, evil beasts, slothful bellies" (Tit. 1:12). Or: although such reasons be fruitless and weak, because, as is said in Psalm 93 (v. 11): "The Lord knoweth the thoughts of men, that they are vain," yet a man's "testament, if it be confirmed, no one despiseth nor addeth to" it, because nothing human has as much power to bind as a man's last will. But someone would be scorning it if he were to say that a man's will, confirmed by his death and by witnesses, had no validity. Therefore, if no one scorns a testament of this kind by saying that it should not be heeded or by modifying it, much less may anyone scorn the testament of God or modify it and weaken it by adding or removing anything: "If any man shall add to these things, God shall add unto him the plagues written in this book: and if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life" (Rev 22:18); "You shall not add to the word that I speak to you, neither shall you take away from it" (Deut 4:2).”

Imported from an open dataset — not yet checked against the printed edition.