Charles Ellicott Commentary Acts 13:39

"and by him every one that believeth is justified from all things, from which ye could not be justified by the law of Moses." — Acts 13:39 (ASV)

And by him.—Literally, in Him, as the sphere in which forgiveness was found, rather than as the instrument through whom it came.

All that believe are justified.—Literally, with a more individualising touch, every one that believes is justified. The latter verb is not found elsewhere in Acts.

It is interesting to note in this, the first recorded example of St. Paul’s teaching, the occurrence of the word which, as time passed on, came to be almost identified with him and with his work. It is clearly used, as interpreted by the “forgiveness of sins” in the context, in its forensic sense, as meaning “acquitted,” “declared not guilty.” (Compare to Note on Matthew 12:37.)

From which you could not be justified by the law of Moses.—These words are full of meaning, as the germ of all that was most characteristic in St. Paul’s later teaching.

The Law, with its high standard of righteousness (Romans 7:12) and its demand of entire obedience, involved sacrifices. While these sacrifices bore witness to the burden of sin, they still had no power to liberate the conscience from its bondage (Hebrews 8:1–3).

This Law had taught him that its function in the spiritual life of humanity was to bring about the knowledge of sin (Romans 7:7), not to emancipate people from it. The sense of freedom from guilt, and therefore of a true life, was to be found, as he had learned by his own experience, through faith in Christ: “The just by faith shall live” (Habakkuk 2:4; Romans 1:17; Galatians 3:11).