4. "The violent is that the origin whereof is from without, without the subject of violence in any way contributing thereto."* Were then the will to be moved by any exterior principle, that motion would be violent. I call that an exterior principle of motion, which moves as an efficient cause, and not as a final cause. But violence is inconsistent with voluntariness. It is impossible therefore for the will to be moved to voluntary action by an exterior principle acting as an efficient cause, but every motion of the will must proceed from within. Now no subsistent creature is in touch with the interior of an intelligent soul: God alone is in such close connexion with the soul, as He alone is cause of its being and maintains it in existence. Therefore by God alone can a motion of the will be efficiently caused.
Hence it is said: The king's heart is in the hand of the Lord: he shall turn it whithersoever he will (Prov. xxi, 1); and, God it is worketh in us both to will and to accomplish according to his good pleasure (Phil. ii, 13).
3.81 : Of the Subordination of Men one to another
3.89 : That the Motion of the Will is caused by God, and not merely by the Power of the Will