From someone who knows the human heart:
Therefore whoever knows well how to distinguish the Gospel from the Law should give thanks to God and know that he is a real theologian. . . .
For so far as the words are concerned, the distinction is easy. But when it comes to experience, you will find the Gospel a rare guest but the Law a constant guest in your conscience, which is habituated to the Law and the sense of sin.
--Martin Luther, Commentary on Galatians, commenting on Gal 2:14, LW: 26:115, 117