They differ in their motives and ends. The believer will not serve sin, because he is alive to God, and dead to sin (Rom 6:6). The legalist forsakes sin, not because he is alive, but that he may live. The believer mortifies sin, because God loves him; but the legalist, that God may love him. The believer mortifies, because God is pacified towards him; the legalist mortifies, that he may pacify God by his mortification. He may go a great length, but it is still that he may have whereof to glory, making his own doing all the foundation of his hope and comfort.
--Ralph Erskine (1685-1752)