Objection 1. It would seem that Christ was not a perfect comprehensor in the first instant of His conception. For merit precedes reward, as fault precedes punishment. But Christ merited in the first instant of His conception, as stated above (Article 3). Since, therefore, the state of comprehension is the principal reward, it seems that Christ was not a comprehensor in the first instant of His conception.
Objection 2. Further, our Lord said (Luke 24:26): "Ought not Christ to have suffered these things, and so to enter into His glory?" But glory belongs to the state of comprehension. Therefore Christ was not in the state of comprehension in the first instant of His conception, when as yet He had not suffered.
Objection 3. Further, what befits neither man nor angel seems proper to God; and therefore is not becoming to Christ as man. But to be always in the state of beatitude befits neither man nor angel: for if they had been created in beatitude, they would not have sinned afterwards. Therefore Christ, as man, was not in the state of beatitude in the first instant of His conception.
On the contrary, It is written (Psalm 64:5): "Blessed is he whom Thou hast chosen, end taken to Thee"; which words, according to the gloss, refer to Christ's human nature, which "was taken by the Word of God unto the unity of Person." But human nature was taken by the Word of God in the first instant of His conception. Therefore, in the first instant of His conception, Christ, as man, was in the state of beatitude; which is to be a comprehensor.
I answer that, As appears from what was said above (Article 3), it was unbecoming that in His conception Christ should receive merely habitual grace without the act. Now, He received grace "not by measure" (John 3:34), as stated above (Question 7, Article 11). But the grace of the "wayfarer," being short of that of the "comprehensor," is in less measure than that of the comprehensor. Wherefore it is manifest that in the first instant of His conception Christ received not only as much grace as comprehensors have, but also greater than that which they all have. And because that grace was not without its act, it follows that He was a comprehensor in act, seeing God in His Essence more clearly than other creatures.
Reply to Objection 1. As stated above (Question 19, Article 3), Christ did not merit the glory of the soul, in respect of which He is said to have been a comprehensor, but the glory of the body, to which He came through His Passion. Wherefore the reply to the Second Objection is clear.
Reply to Objection 3. Since Christ was both God and man, He had, even in His humanity, something more than other creatures--namely, that He was in the state of beatitude from the very beginning.
Source: Summa Theologica (New Advent)