72 Far be it from us to imagine vicissitudes of bodily change in the Father and Son, as though the Father sometimes spoke to the Son, and sometimes was silent. We remember, indeed, that a voice was sometimes uttered from heaven for us, that the power of the Father's words might confirm for us the mystery of the Son, as the Lord says, This voice has not come from Heaven for My sake but for your sakes. But the divine nature can dispense with the various combinations necessary for human functions, the motion of the tongue, the adjustment of the mouth, the forcing of the breath, and the vibration of the air.
God is a simple Being: we must understand Him by devotion, and confess Him by reverence. He is to be worshipped, not pursued by our senses, for a conditioned and weak nature cannot grasp with the guesses of its imagination the mystery of an infinite and omnipotent nature. In God is no variability, no parts, as of a composite divinity, that in Him will should follow inaction, speech silence, or work rest, or that He should not will, without passing from some other mental state to volition, or speak, without breaking the silence with His voice, or act, without going forth to labour.
He is not subject to the laws of nature, for nature has received its law from Him: He never suffers weakness or change when He acts, for His power is boundless, as the Lord said, Father, all things are possible unto You. He can do more than human sense can conceive. The Lord does not deprive even Himself of the quality of omnipotence, for He says, What things soever the Father does, these the Son also does in like manner. Nothing is difficult, when there is no weakness; for only a power which is weak to effect, knows the need of effort. The cause of difficulty is the weakness of the motive force; a force of limitless power rises above the conditions of impotence.
Source: On the Trinity (New Advent)