Wishing to give a reason for the Lord's answer to the apostles, he assigns the one received to Christ's tenderness. Then when another reason is supplied by others he confesses that it is true; for the Lord spoke it by reason of His human feelings. Hence he gathers that the knowledge of the Father and the Son is equal, and that the Son is not inferior to the Father. After having set beside the text, in which He is said to be inferior, another whereby He is declared to be equal, he censures the rashness of the Arians in judging about the Son, and shows that whilst they wickedly make Him to be inferior, He is rightly called a Stone by Himself.
219. We have been taught therefore that the Son of God is not ignorant of the future. If they confess this, I too— that I may now answer why He declared that neither angels, nor the Son, but only the Father knows— call to mind His wonted love for His disciples also in this passage, and His grace, which by its very frequency ought to have been known to all. For the Lord, filled with deep love for His disciples, when they asked from Him what He thought unprofitable for them to know, prefers to seem ignorant of what He knows, rather than to refuse an answer. He loves rather to provide what is useful for us, than to show His own power.
220. There are, however, some not so faint-hearted as I. For I would rather fear the deep things of God, than be wise. There are some, however, relying on the words: “And Jesus increased in age and in wisdom and in favour with God and man,” who boldly say, that according to His Godhead indeed He could not be ignorant of the future, but that in His assumption of our human state He said that He as Son of Man was in ignorance before His crucifixion. For when He speaks of the Son, He does not speak as it were of another; for He Himself is our Lord the Son of God and the Son of a Virgin. But by a word which embraces both, He guides our mind, so that He as Son of Man according to His adoption of our ignorance and growth of knowledge, might be believed as yet not fully to have known all things. For it is not for us to know the future. Thus He seems to be ignorant in that state in which He makes progress. For how does He progress according to His Godhead, in Whom the fullness of the Godhead dwells? Or what is there which the Son of God does not know, Who said: “Why do you think evil in your hearts?” How does He not know, of Whom Scripture says: “But Jesus knew their thoughts”?
221. This is what others say, but I— to return to my former point, where I stated it was written of the Father: “It may be they will reverence My Son,”— I think indeed this was written in order that the Father, as He was speaking of men, might also seem to have spoken with human feelings. But still more am I inclined to think that the Son Who went about with men, and lived the life of man, and took upon Him our flesh, assumed also our feelings; so that after our ignorance He might say He knew not, though there was not anything He did not know. For though He seemed to be a man in the reality of His body, yet was He Life, and Light, and virtue came out of Him, to heal the wounds of the injured by the power of His Majesty.
222. You see then that this matter has been solved for you, since the saying of the Son is referred to the assumption of our state in its fullness, and it was thus written concerning the Father, in order that you might cease to cavil at the Son.
223. There was nothing then of which the Son of God was ignorant, for there was nothing of which the Father was ignorant. But if the Son was ignorant of nothing, as we now conclude, let them say in what respect they wish Him to seem to be inferior. If God has begotten a Son inferior to Himself, He has granted Him less. If He has granted Him less, He either wished to give less, or could only give less. But the Father is neither weak nor envious, seeing that there was neither will nor power before the Son. For wherein is He inferior, Who has all things even as the Father has them? He has received all things from the Father by right of His Generation, and has shown forth the Father wholly by the glory of His Majesty.
224. It is written, they say: “For the Father is greater than I.” It is also written: “He thought it not robbery to be equal with God.” It is written again that the Jews wished to kill Him, because He said He was the Son of God, making Himself equal with God. It is written: “I and My Father are one.” They read “one,” they do not read “many.” Can He then be both inferior and equal in the same Nature? Nay, the one refers to His Godhead, the other to His flesh.
225. They say He is inferior: I ask who has measured it, who is of so overweening a heart, as to place the Father and the Son before his judgment seat to decide upon which is the greater? “My heart is not haughty nor are my eyes raised unto vanity,” says David. King David feared to raise his heart in pride in human affairs, but we raise ours even in opposition to the divine secrets. Who shall decide about the Son of God? Thrones, dominions, angels, powers? But archangels give attendance and serve Him, cherubim and seraphim minister to Him and praise Him. Who then decides about the Son of God, on reading that the Father Himself knows the Son, but will not judge Him. “For no man knows the Son, but the Father.” “Knows” it says, not “judges.” It is one thing to know, another to judge. The Father has knowledge in Himself. The Son has no power superior to Himself. And again: “No man knows the Father, but the Son;” and He Himself knows the Father, as the Father knows Him.
226. But you say that He said He was inferior, He said also He was a Stone. You say more and yet you impiously attack Him. I say less and with reverence add to His honour. You say He is inferior and confess Him to be above the angels. I say He is less than the angels, yet do not take from His honour; for I do not refute His Godhead, but I do proclaim His pity
Source: On the Christian Faith (De fide) (New Advent)