Jamieson, Fausset and Brown on Romans 3:21-23

Ro 3:21-26. God's Justifying Righteousness through Faith in Jesus Christ, Alike Adapted to Our Necessities and Worthy of Himself.

21-23. But now the righteousness of God--(See on Ro 1:17).

without the law--that is, a righteousness to which our obedience to the law contributes nothing whatever (Ro 3:28; Ga 2:16).

is manifested, being witnessed--attested.

by the law and the prophets--the Old Testament Scriptures. Thus this justifying righteousness, though new, as only now fully disclosed, is an old righteousness, predicted and foreshadowed in the Old Testament.