Jerome, Commentary on Galatians, [J.P. Migne, Editor]. Patrologiae Tomus XXVI. Paris: D’Ambroise, Pres La Barriere D’Enfer, ou Petit-Montrouge, 1845. pp. 307-438.
Jerome observbes that Paul had many credentials which would allow him to exercise authority over the thinking of the Galatians, but that in Galatians 3:15 he speaks ‘as a human” - in simple terms (Jerome, Galatians, 364). Jerome notes this was also Paul’s attitude as expressed in his letters to the Corinthians. The heart of Paul’s statement here is that God will bless the singular seed of Abraham. Jerome sees this as different from God’s Word, which is scattered to many. Here the promise is regarding one seed of Abraham, whom Jerome recognizes as Jesus (Jerome, Galatians, 365). Jerome continues with a brief history of God delivering His promise to just one of multiple offspring, but concludes that in the end the singular chosen offspring was a blessing to all nations. This blessing is by grace, not by the law, which was passed to all.
In verses 19-20, Paul points out that the Law was put into force because of transgressions, while the promise was purely a matter of promise from the one God. Jerome points out numerous events in the history of Israel where transgression could be seen (Jerome, Galatians, 366). He further observes that Christ was present with the Father as the “Word God” from the beginning and that his presence in word has been shown many times. Jerome points out that Scripture is very clear that Christ speaks as the almighty God and that he is the one who spoke all God’s Law into force (Jerome, Galatians, 367).