4 “But,” says he, “the Father commands, that the Son may execute.” Carnal indeed is your conceit, but without prejudice to the truth, I grant it to you. Lo, the Father commands, the Son obeys; is the Son therefore not of the same Nature, because the One commands, and the Other obeys? Give me two men, father and son; they are two men: he that commands is a man; he that obeys is a man; he that commands and he that obeys have one and the same nature. Does not he that commands, beget a son of his own nature?
Does he who obeys, by obeying lose his nature? Now take for the present, as you thus take two men, the Father commanding, the Son obeying, yet God and God. But the first two together are two men, the Latter together is but One God; this is a divine miracle. Meanwhile if you would that with you I acknowledge the obedience, do you first with me acknowledge the Nature. The Father begot That which Himself is. If the Father begot ought else than what Himself is, He did not beget a true Son.
The Father says to the Son, “From the womb before the day-star, I begot You.” What is, “before the day-star”? By the day-star times are signified. So then before times, before all that is called “before;” before all that is not, or before all that is. For the Gospel does not say, “In the beginning God made the Word;” as it is said, “In the beginning God made the Heaven and the earth;” or, “In the beginning was the Word born;” or, “In the beginning God begot the Word.” But what says it?
“He was, He was, He was.” You hear, “He was;” believe. “In the beginning was the Word, and the Word was with God, and the Word was God.” So often do you hear, “Was:” seek not for time, for that He always “was.” He then who always was, and was always with the Son, for that God is able to beget without you; He said to the Son, “From the womb before the day-star I begot You.” What is from the womb? Had God a womb? Shall we imagine that God was fashioned with bodily members? God forbid! And why said He, “From the womb,” but that it might be understood that He begot Him of His Own Substance? So then from the womb came forth That which Himself was who begot. For if He who begot was one thing, and another came forth out of the womb; it were a monster, not a Son.
Source: Sermons on Selected Lessons of the New Testament (New Advent)