“Attend, then, carefully, to the apostle while in his Epistle to the Romans he explains and clearly enough shows that what he wrote to the Corinthians, “The letter kills, but the spirit gives life,” 2 Corinthians 3:6 must be understood in the sense which we have already indicated—that the letter of the law, which teaches [...]

“Here, perhaps, it may be said by that presumption of man, which is ignorant of the righteousness of God, and wishes to establish one of its own, that the apostle quite properly said, “For by the law shall no man be justified,” Romans 3:20 inasmuch as the law merely shows what one ought to do, [...]

http://gnesiolutheran.com/ambrose-on-justification-a-study-in-the-catholicity-of-lutheran-theology/

VERSE 11. But that no man is justified by the law in the sight of God, it is evident: for, “The just shall live by faith.”

The Apostle draws into his argument the testimony of the Prophet Habakkuk: “The just shall live by his faith.” This passage carries much weight because it eliminates the Law [...]

Ver. 12. “And the Law is not of faith; but He that does them shall live in them.”

For the Law requires not only Faith but works also, but grace saves and justifies by Faith. Ephesians 2:8

You see how he proves that they are under the curse who cleave to the Law, because it [...]

“But the law is not of faith, rather ‘The one who does them shall live by them’ Christ redeemed us from the curse of the law by becoming a curse for us-for it is written-’Cursed is everyone who is hanged on a tree’” (Galatians 3:12-13).