Objection 1. It would seem that the soul of Christ does not see the Word more perfectly than does any other creature. For the perfection of knowledge depends upon the medium of knowing; as the knowledge we have by means of a demonstrative syllogism is more perfect than that which we have by means of a probable syllogism. But all the blessed see the Word immediately in the Divine Essence Itself, as was said in I, 12, 2. Therefore the soul of Christ does not see the Word more perfectly than any other creature.
Objection 2. Further, the perfection of vision does not exceed the power of seeing. But the rational power of a soul such as is the soul of Christ is below the intellective power of an angel, as is plain from Dionysius (Coel. Hier. iv). Therefore the soul of Christ did not see the Word more perfectly than the angels.
Objection 3. Further, God sees His Word infinitely more perfectly than does the soul of Christ. Hence there are infinite possible mediate degrees between the manner in which God sees His Word, and the manner in which the soul of Christ sees the Word. Therefore we cannot assert that the soul of Christ sees the Word or the Divine Essence more perfectly than does every other creature.
On the contrary, The Apostle says (Ephesians 1:20-21) that God set Christ "on His right hand in the heavenly places, above all principality and power and virtue and dominion and every name that is named not only in this world, but also in that which is to come." But in that heavenly glory the higher anyone is the more perfectly does he know God. Therefore the soul of Christ sees God more perfectly than does any other creature.
I answer that, The vision of the Divine Essence is granted to all the blessed by a partaking of the Divine light which is shed upon them from the fountain of the Word of God, according to Sirach 1:5: "The Word of God on high is the fountain of Wisdom." Now the soul of Christ, since it is united to the Word in person, is more closely joined to the Word of God than any other creature. Hence it more fully receives the light in which God is seen by the Word Himself than any other creature. And therefore more perfectly than the rest of creatures it sees the First Truth itself, which is the Essence of God; hence it is written (John 1:14): "And we saw His glory, the glory as it were of the Only-begotten of the Father," "full" not only of "grace" but also of "truth."
Reply to Objection 1. Perfection of knowledge, on the part of the thing known, depends on the medium; but as regards the knower, it depends on the power or habit. And hence it is that even amongst men one sees a conclusion in a medium more perfectly than another does. And in this way the soul of Christ, which is filled with a more abundant light, knows the Divine Essence more perfectly than do the other blessed, although all see the Divine Essence in itself.
Reply to Objection 2. The vision of the Divine Essence exceeds the natural power of any creature, as was said in I, 12, 4. And hence the degrees thereof depend rather on the order of grace in which Christ is supreme, than on the order of nature, in which the angelic nature is placed before the human.
Reply to Objection 3. As stated above (Question 7, Article 12), there cannot be a greater grace than the grace of Christ with respect to the union with the Word; and the same is to be said of the perfection of the Divine vision; although, absolutely speaking, there could be a higher and more sublime degree by the infinity of the Divine power.
Source: Summa Theologica (New Advent)