If the promises communicated blessing, and the law subjected to cursing, then obviously, if we had accepted it as having force, it would have destroyed the promises of God, which give blessing. But let it not be so. Listen further in order.
Gal. 3:21. For if a law had been given that could give life, then righteousness would truly have been from the law;
Then, he says, the law would have been stronger than faith, would have imparted blessing and justified man, if it had been able to give life and save. But now it rather kills, since it cannot free from sins. How then can the law overcome faith, which has the power to give life through baptism, and to bless and justify?
Gal. 3:22. But the Scripture has concluded all things (τα πάντα) under sin, that the promise might be given to those who believe through faith in Jesus Christ.
The Law, he says, did not have the power to free from sins, but contributed to "shutting up" people under sin, that is, to show them as sinners and compel them to desire the remission of sins and turn to Christ, who is able to grant it. And since the Jews, not feeling the full weight of their sins, did not desire their forgiveness either, God gave the Law, which shuts them in, that is, presses and oppresses them with reproofs, declares them sinners, and urges them to seek a way to obtain forgiveness. And this way is faith in Christ, through which we receive blessing and justification.
Gal. 3:23. But before faith came, we were kept under the guard of the law, until the time when faith was to be revealed.
The Law, he says, provided great safety to those who were under its protection, because it restrained them from many sins and was like a wall, surrounding people and leading them to faith. In what way? By exposing sins, but not having the power to free from them, it necessarily pointed to the justifying faith, which existed even in ancient times, but in a hidden manner, and was openly revealed later, when God also appeared in the flesh.
Gal. 3:24. So then, the law was our schoolmaster unto Christ, that we might be justified by faith;
As a tutor protects a youth from everything harmful and helps him receive the teacher's instructions with all attentiveness and diligence, so too the law cultivated proper virtue in its followers and led them to the teacher – Christ, by its reproofs and indications of sins arousing in them the desire to seek the One who grants forgiveness and justifies by faith. Therefore, let those who slander the law be ashamed – for neither does the tutor stand in opposition to the teacher, nor the law to the New Testament.
Gal. 3:25. But with the coming of faith, we are no longer under the guidance of a tutor.
Gal. 3:26. For you are all sons of God through faith in Christ Jesus;
With the coming of faith, which makes one a "perfect man," we, he says, can no longer be under the guidance of a tutor, as having become perfect through it and having outgrown childhood. Since through faith we have become perfect men, it is clear from this that we have also become sons of God through faith in Christ. Such is the train of thought. Of course, one who has been deemed worthy to be a son of God is not imperfect and not an infant. Therefore it would be strange for those who have become men to submit to the guidance of the law, just as it would be to use a lamp when day has come and the sun is shining. Notice, above he said that faith makes one sons of Abraham, but now — sons of God. So much can it do.
Gal. 3:27. All you who were baptized into Christ have put on Christ.
Defining in what way we are sons of God, he says: through baptism. But he did not say: you who were baptized became children of God, as the sequence would seem to require, — but far more expressively: you have put on Christ. And if we have put on Christ, the Son of God, and have been made like unto Him, it means we have been brought into one kinship, into one image, having become by grace what He is by nature.
Gal. 3:28. There is neither Jew nor Greek; there is neither slave nor free; there is neither male nor female: for you are all one in Christ Jesus.
Each of the baptized, he says, has cast off his natural distinctions; all have received one type and one image, not of an Angel, but of the Lord Himself, manifesting Christ in themselves. So that we are all one in Christ Jesus, precisely insofar as we have one imprinted image of Christ, or insofar as we are one body, having one head, Christ.
Gal. 3:29. And if you are Christ's, then you are Abraham's seed, and heirs according to the promise.
Since earlier he said that the seed of Abraham, through which the nations shall be blessed, is Christ, to Whom precisely the promises were given, and also pointed out that you too bear the image of Christ, he now concludes: therefore, you too are the seed of Abraham and heirs of the promised blessing. How then after this do you hold to the law — you who received the blessing through having put on Christ and become like Him, and thereby became the seed of Abraham?