The Apostle Paul
Galatians 2:16BSB·traditional attribution

know that a man is not justified by works of the law, but by faith in Jesus Christ. So we, too, have believed in Christ Jesus, that we may be justified by faith in Christ and not by works of the law, because by works of the law no one will be justified.

John Calvin Reformed @genevareformer

16. But by the faith of Jesus Christ. He does not merely state that ceremonies, or works of any kind, are insufficient without the assistance of faith, but meets their denial by a statement admitting of no exception, as if he had said, “Not by works, but by the Gift of Christ alone.” In any other point of view, the sentiment would have been trivial...

Matthew Henry Presbyterian @wholebiblehenry

I. From the account which Paul gives of what passed between him and the other apostles at Jerusalem, the Galatians might easily discern both the falseness of what his enemies had insinuated against him and their own folly and weakness in departing from that gospel which he had preached to them.

Commenting on Galatians 2:11-21

John Gill Reformed Baptist @doctorgill

Knowing that a man is not justified by the works of the law,.... That is, Peter, Paul, Barnabas, and other believing Jews knew this, and that from the law itself, which requires perfect and sinless obedience, and accuses, holds guilty, and adjudges to condemnation and death for the least failure, both as to matter or manner of duty; and from the prophets, which declare that...