48 But, my opponent, the unity of Their nature is such, that the several action of Each implies the conjoint action of Both, and Their joint activity a several activity of Each. Conceive the Son acting, and the Father acting through Him. He acts not of Himself, for we have to explain how the Father abides in Him. He acts in His own Person, for in accordance with His birth as the Son, He does Himself what is pleasing. His acting not of Himself would prove Him weak, were it not the case that He so acts that what He does is pleasing to the Father. But He would not be in the unity of the divine nature, if the deeds which He does, and wherein He pleases, were not His own, and He were merely prompted to action by the Father abiding in Him. The Father then in abiding in Him, teaches Him, and the Son in acting, acts not of Himself; while, on the other hand, the Son, though not acting of Himself, acts Himself, for what He does is pleasing. Thus is the unity of Their nature retained in Their action, for the One, though He acts Himself, does not act of Himself, while the Other, Who has abstained from action, is yet active.
Source: On the Trinity (New Advent)