Objection 1. It would seem that the soul of Christ does not know all things in the Word. For it is written (Mark 13:32): "But of that day or hour no man knoweth, neither the angels in heaven nor the Son, but the Father." Therefore He does not know all things in the Word.
Objection 2. Further, the more perfectly anyone knows a principle the more he knows in the principle. But God sees His Essence more perfectly than the soul of Christ does. Therefore He knows more than the soul of Christ knows in the Word. Therefore the soul of Christ does not know all things in the Word.
Objection 3. Further, the extent depends on the number of things known. If, therefore, the soul of Christ knew in the Word all that the Word knows, it would follow that the knowledge of the soul of Christ would equal the Divine knowledge, i.e. the created would equal the uncreated, which is impossible.
On the contrary, on Apocalypse 5:12, "The Lamb that was slain is worthy to receive... divinity and wisdom," a gloss says, i.e. "the knowledge of all things."
I answer that, When it is inquired whether Christ knows all things in the Word, "all things" may be taken in two ways: First, properly, to stand for all that in any way whatsoever is, will be, or was done, said, or thought, by whomsoever and at any time. And in this way it must be said that the soul of Christ knows all things in the Word. For every created intellect knows in the Word, not all simply, but so many more things the more perfectly it sees the Word. Yet no beatified intellect fails to know in the Word whatever pertains to itself. Now to Christ and to His dignity all things to some extent belong, inasmuch as all things are subject to Him. Moreover, He has been appointed Judge of all by God, "because He is the Son of Man," as is said John 5:27; and therefore the soul of Christ knows in the Word all things existing in whatever time, and the thoughts of men, of which He is the Judge, so that what is said of Him (John 2:25), "For He knew what was in man," can be understood not merely of the Divine knowledge, but also of His soul's knowledge, which it had in the Word. Secondly, "all things" may be taken widely, as extending not merely to such things as are in act at some time, but even to such things as are in potentiality, and never have been nor ever will be reduced to act. Now some of these are in the Divine power alone, and not all of these does the soul of Christ know in the Word. For this would be to comprehend all that God could do, which would be to comprehend the Divine power, and, consequently, the Divine Essence. For every power is known from the knowledge of all it can do. Some, however, are not only in the power of God, but also in the power of the creature; and all of these the soul of Christ knows in the Word; for it comprehends in the Word the essence of every creature, and, consequently, its power and virtue, and all things that are in the power of the creature.
Reply to Objection 1. Arius and Eunomius understood this saying, not of the knowledge of the soul, which they did not hold to be in Christ, as was said above (Question 9, Article 1), but of the Divine knowledge of the Son, Whom they held to be less than the Father as regards knowledge. But this will not stand, since all things were made by the Word of God, as is said John 1:3, and, amongst other things, all times were made by Him. Now He is not ignorant of anything that was made by Him.
He is said, therefore, not to know the day and the hour of the Judgment, for that He does not make it known, since, on being asked by the apostles (Acts 1:7), He was unwilling to reveal it; and, on the contrary, we read (Genesis 22:12): "Now I know that thou fearest God," i.e. "Now I have made thee know." But the Father is said to know, because He imparted this knowledge to the Son. Hence, by saying but the Father, we are given to understand that the Son knows, not merely in the Divine Nature, but also in the human, because, as Chrysostom argues (Hom. lxxviii in Matth.), if it is given to Christ as man to know how to judge--which is greater--much more is it given to Him to know the less, viz. the time of Judgment. Origen, however (in Matth. Tract. xxx), expounds it of His body, which is the Church, which is ignorant of this time. Lastly, some say this is to be understood of the adoptive, and not of the natural Son of God.
Reply to Objection 2. God knows His Essence so much the more perfectly than the soul of Christ, as He comprehends it. And hence He knows all things, not merely whatever are in act at any time, which things He is said to know by knowledge of vision, but also what ever He Himself can do, which He is said to know by simple intelligence, as was shown in I, 14, 9. Therefore the soul of Christ knows all things that God knows in Himself by the knowledge of vision, but not all that God knows in Himself by knowledge of simple intelligence; and thus in Himself God knows many more things than the soul of Christ.
Reply to Objection 3. The extent of knowledge depends not merely on the number of knowable things, but also on the clearness of the knowledge. Therefore, although the knowledge of the soul of Christ which He has in the Word is equal to the knowledge of vision as regards the number of things known, nevertheless the knowledge of God infinitely exceeds the knowledge of the soul of Christ in clearness of cognition, since the uncreated light of the Divine intellect infinitely exceeds any created light received by the soul of Christ; although, absolutely speaking, the Divine knowledge exceeds the knowledge of the soul of Christ, not only as regards the mode of knowing, but also as regards the number of things known, as was stated above.
Source: Summa Theologica (New Advent)