In 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