“The Holy Scriptures, especially the New Testament, often mention faith in Christ and say that whoever believes in him is saved, does not perish, is not judged, has eternal life, and so on (see John 3:16 and 5:24). Saying that people who believe in him are condemned because they have faith without works is to pervert everything, making Christ a destroyer and a murderer, and Moses a saviour. I admit that our adversaries do not use these exact words, but this is in fact what they teach. They say that faith in Christ does not make us free from sin, but only faith combined with love. This is to say that Christ leaves us in our sins and in the wrath of God and makes us guilty of eternal death, whereas if you keep the law, faith justifies you because it has works, without which faith is no help. Therefore, works justify, and not faith, they claim. What pernicious and cursed teaching this is!
“Paul bases his argument on an impossibility. If we are justified in Christ and yet are still sinners and can be justified only by some means other than Christ—namely, by the law—then Christ cannot justify us but only accuses and condemns us. And it then follows that Christ died in vain, and this passage and others (such as John 1:29and 3:16) are not true. The whole Scripture is then false when it tells us that Christ is the justifier and Saviour of the world. If we are still sinners after we have been justified by Christ, it follows that those who fulfill the law are justified without Christ. If this is true, then we are heretics, professing the name and Word of God outwardly but in reality denying Christ and his Word. It is therefore great impiety to say that faith does not justify unless it is combined with works of love. If faith and works together justify us, then Paul’s words are not true when he says we are justified by faith in Christ and not by observing the law (verse 16).”
“To teach that faith in Christ does not justify us unless we observe the law is to make Christ a minister of sin—that is, a teacher of the law, teaching the very same doctrine that Moses did. Thus Christ is no Saviour, no giver of grace, but a cruel tyrant who, like Moses, requires things that none of us can do. But the Gospel is a preaching of Christ who forgives sins, gives grace, and justifies and saves sinners. There are commandments in the Gospel, but they are not the Gospel but expositions of the law, and they depend on the Gospel.”
Luther, M. (1998). Galatians. The Crossway classic commentaries (93–95). Wheaton, Ill.: Crossway Books.