Therefore these two things (as I do often repeat), to wit the law and the promise, must be diligently distinguished. For in time, in place, and in person, and generally in all other circumstances, they are separate as far asunder as heaven and earth... so that the law may have dominion over the flesh, and the promise may sweetly (and comfortably) reign in the conscience... But now, if thou confound and mingle these two together and place the law in the conscience, and the promise of liberty in the flesh thou makest a confusion... so that thou shalt not know what the law, what the promise, what sin, or what righteousness is.

From Martin Luther's commentary on Galatians