Galatians 3:11 (ESV) … “Now it is evident that no one is justified before God by the law, for “The righteous shall live by faith.”
If any man who attempts to earn right-standing (justification) before God by law-keeping finds himself unable to keep it all and is thus condemned, it is obvious justification was never intended to be achieved by the Law. That point Paul now stated with certainty: “No man is justified by the law in the sight of God.” This no man includes any person who ever has lived or will live, whether in Old Testament or New Testament times. Paul was stating a universal and timeless rule. God never intended anyone to obtain justification by the Law, for then only the sinless would be justified and sinners could never be saved. But all have sinned.
Paul again gives evidence of his point by turning to the very Old Testament in which the Law was established. This time he quoted one of the prophets (see Habakkuk 2:4) to the effect that “The just shall live by faith.” The word “just” is singular here and refers to any person who is justified. The whole sentence means that one can only live in a justified state, one can only experience justification, by faith. To be justified is to live; to be guilty is to be under the curse of death. A person can only be found innocent, and thus live, by faith.
You see how powerful was Paul’s point: He was not merely stating what is true now, but what has always been true. The Judaizers were not only wrong about the present method of salvation, but about the past too. Even in Old Testament days, Paul was saying a man experienced justification only by faith. No one ever became spiritually a son of Abraham except by this one plan.