Luke 2:52 reads, "And Jesus advanced in wisdom, and age, and grace with God and men." But did Christ actually become more holy during His lifetime?
The short answer is no. Haydock's Catholic Bible Commentary from 1859 cites Pope St. Gregory the Great when explaining that Christ did not grow in wisdom or grace in any real sense but, rather, gradually manifested both over time as was appropriate to His salvific mission. The commentary reads: "In the same manner, also He increased in grace, by displaying, as He advanced in age, the gifts of grace with which He was endowed."
Commenting on Luke 2:52 in his Summa Theologica, St. Thomas Aquinas similarly teaches that Christ didn't grow in grace, but that He simply unveiled that grace more fully over time:
Anyone may increase in wisdom and grace in two ways. First inasmuch as the very habits of wisdom and grace are increased; and in this way Christ did not increase. Secondly, as regards the effects, i.e., inasmuch as they do wiser and greater works; and in this way Christ increased in wisdom and grace even as in age, since in the course of time, He did more perfect works, (ST III, q.7, a.12, ad. 3).
Of course, Christ is a divine person. As God, He's the source of sanctity and, therefore, can't become more holy. But what about Christ's human nature: Could it become holier over time?
Again, no. During life, God gradually confers holiness to men via the Holy Spirit in what's called the divine indwelling. But with the Incarnation, as St. Thomas relates, Christ completely sanctified His human nature by perfectly uniting it to His divine nature in the hypostatic union.
Another reason that Christ's human nature couldn't grow in grace, St. Thomas explains, was that, like the blessed in Heaven, Christ always beheld the beatific vision in His human mind, "hence there could have been no increase of grace in Him, as there could be none in the rest of the blessed" (ST III, q.7, a.12, co.).
Plunge into the deep mystery of Christ by watching Church Militant's Premium show The One True Faith—Jesus Christ.