Paul undertakes to explain the difference between the righteousness of the Law and the righteousness of faith. The righteousness of the Law is the fulfillment of the Law according to the passage: “The man that doeth them shall live in them.” The righteousness of faith is to believe the Gospel according to the passage: “The just shall live by faith.” The Law is a statement of debit, the Gospel a statement of credit. By this distinction Paul explains why charity which is the commandment of the Law cannot justify, because the Law contributes nothing to our justification.
Indeed, works do follow after faith, but faith is not therefore a meritorious work. Faith is a gift. The character and limitations of the Law must be rigidly maintained.
When we believe in Christ we live by faith. When we believe in the Law we may be active enough but we have no life. The function of the Law is not to give life; the function of the Law is to kill. True, the Law says: “The man that doeth them shall live in them.” But where is the person who can do “them,” i.e., love God with all his heart, soul, and mind, and his neighbor as himself?
Paul has nothing against those who are justified by faith and therefore are true doers of the Law. He opposes those who think they can fulfill the Law when in reality they can only sin against the Law by trying to obtain righteousness by the Law. The Law demands that we fear, love, and worship God with a true faith. The law-workers fail to do this. Instead, they invent new modes of worship and new kinds of works which God never commanded. They provoke His anger according to the passage: “But in vain they do worship me, teaching for doctrines the commandments of men.” (Matthew 15:9.) Hence, the law-righteous workers are downright rebels against God, and idolaters who constantly sin against the first commandment. In short, they are no good at-all though outwardly they seem to be extremely solicitous of the honor of God.
We who are justified by faith as the saints of old, may be under the Law, but we are not under the curse of the Law because sin is not imputed to us for Christ’s sake. If the Law cannot be fulfilled by the believers, if sin continues to cling to them despite their love for God, what can you expect of people who are not yet justified by faith, who are still enemies of God and His Word, like the unbelieving law-workers? It goes to show how impossible it is for those who have not been justified by faith to fulfill the Law.
Law, Grace, & Daily Living 