Objection 1. It would seem that in Christ there was no knowledge except the Divine. For knowledge is necessary that things may be known thereby. But by His Divine knowledge Christ knew all things. Therefore any other knowledge would have been superfluous in Him.
Objection 2. Further, the lesser light is dimmed by the greater. But all created knowledge in comparison with the uncreated knowledge of God is as the lesser to the greater light. Therefore there shone in Christ no other knowledge except the Divine.
Objection 3. Further, the union of the human nature with the Divine took place in the Person, as is clear from 2, 2. Now, according to some there is in Christ a certain "knowledge of the union," whereby Christ knew what belongs to the mystery of Incarnation more fully than anyone else. Hence, since the personal union contains two natures, it would seem that there are not two knowledges in Christ, but one only, pertaining to both natures.
On the contrary, Ambrose says (De Incarnat. vii): "God assumed the perfection of human nature in the flesh; He took upon Himself the sense of man, but not the swollen sense of the flesh." But created knowledge pertains to the sense of man. Therefore in Christ there was created knowledge.
I answer that, As said above (Article 5), the Son of God assumed an entire human nature, i.e. not only a body, but also a soul, and not only a sensitive, but also a rational soul. And therefore it behooved Him to have created knowledge, for three reasons. First, on account of the soul's perfection. For the soul, considered in itself, is in potentiality to knowing intelligible things. since it is like "a tablet on which nothing is written," and yet it may be written upon through the possible intellect, whereby it may become all things, as is said De Anima iii, 18. Now what is in potentiality is imperfect unless reduced to act. But it was fitting that the Son of God should assume, not an imperfect, but a perfect human nature, since the whole human race was to be brought back to perfection by its means. Hence it behooved the soul of Christ to be perfected by a knowledge, which would be its proper perfection. And therefore it was necessary that there should be another knowledge in Christ besides the Divine knowledge, otherwise the soul of Christ would have been more imperfect than the souls of the rest of men. Secondly, because, since everything is on account of its operation, as stated De Coel. ii, 17, Christ would have had an intellective soul to no purpose if He had not understood by it; and this pertains to created knowledge. Thirdly, because some created knowledge pertains to the nature of the human soul, viz. that whereby we naturally know first principles; since we are here taking knowledge for any cognition of the human intellect. Now nothing natural was wanting to Christ, since He took the whole human nature, as stated above (Article 5). And hence the Sixth Council [Third Council of Constantinople, Act. 4] condemned the opinion of those who denied that in Christ there are two knowledges or wisdoms.
Reply to Objection 1. Christ knew all things with the Divine knowledge by an uncreated operation which is the very Essence of God; since God's understanding is His substance, as the Philosopher proves (Metaph. xii, text. 39). Hence this act could not belong to the human soul of Christ, seeing that it belongs to another nature. Therefore, if there had been no other knowledge in the soul of Christ, it would have known nothing; and thus it would have been assumed to no purpose, since everything is on account of its operation.
Reply to Objection 2. If the two lights are supposed to be in the same order, the lesser is dimmed by the greater, as the light of the sun dims the light of a candle, both being in the class of illuminants. But if we suppose two lights, one of which is in the class of illuminants and the other in the class of illuminated, the lesser light is not dimmed by the greater, but rather is strengthened, as the light of the air by the light of the sun. And in this manner the light of knowledge is not dimmed, but rather is heightened in the soul of Christ by the light of the Divine knowledge, which is "the true light which enlighteneth every man that cometh into this world," as is written John 1:9.
Reply to Objection 3. On the part of what are united we hold there is a knowledge in Christ, both as to His Divine and as to His human nature; so that, by reason of the union whereby there is one hypostasis of God and man, the things of God are attributed to man, and the things of man are attributed to God, as was said above (3, 1, 6). But on the part of the union itself we cannot admit any knowledge in Christ. For this union is in personal being, and knowledge belongs to person only by reason of a nature.
Source: Summa Theologica (New Advent)