The Devil can so completely assume the human form, when he wants to deceive us, that we may well lie with what seems to be a woman, of real flesh and blood, and yet all the while 'tis only the Devil in the shape of a woman. 'Tis the same with women, who may think that a man is in bed with them, yet 'tis only the Devil; and...the result of this connection is oftentimes an imp of darkness, half mortal, half devil.
Martin LutherIn Romans 7, St. Paul says, "The law is spiritual." What does that mean? If the law were physical, then it could be satisfied by works, but since it is spiritual, no one can satisfy it unless everything he does springs from the depths of the heart. But no one can give such a heart except the Spirit of God, who makes the person be like the law, so that he actually conceives a heartfelt longing for the law and henceforward does everything, not through fear or coercion, but from a free heart.
Martin Luther