13 And was it needful for the Lord to be baptized? I instantly reply to any one who asks this question: Was it needful for the Lord to be born? Was it needful for the Lord to be crucified? Was it needful for the Lord to die? Was it needful for the Lord to be buried? If He undertook for us so great humiliation, might He not also receive baptism? And what profit was there that he received the baptism of a servant? That you might not disdain to receive the baptism of the Lord.
Give heed, beloved brethren. Certain catechumens were to arise in the Church of higher grace. It sometimes comes to pass that you see a catechumen who practises continence, bids farewell to the world, renounces all his possessions, distributing them to the poor; and although but a catechumen, instructed in the saving doctrine better, perhaps, than many of the faithful. It is to be feared regarding such an one that he may say to himself about holy baptism, whereby sins are remitted, What more shall I receive?
Behold, I am better than this faithful man, and this—having in his mind those among the faithful who are either married, or who are perhaps ignorant, or who keep possession of their property, while he has given his to the poor—and considering himself better than those who have been already baptized, he deigns not to come to baptism, saying, Am I to receive what this man has, and this thinking of persons whom he despises, and, as it were, considers it an indignity to receive that which inferiors have received, because he appears to himself to be already better than they; and, nevertheless, all his sins are upon him, and without coming to saving baptism, wherein all sins are remitted, he cannot, with all his excellence, enter into the kingdom of heaven.
But the Lord, in order to invite such excellence to his baptism, that sins might be remitted, Himself came to the baptism of His servant; and although He had no sin to be remitted, nor was there anything in Him that needed to be washed, He received baptism from a servant; and by so doing, addressed Himself to the son carrying himself proudly, and exalting himself, and disdaining, perhaps, to receive along with the ignorant that from which salvation comes to him, and said to him: How do you extend yourself? How do you exalt yourself? How great is your excellence? How great is your grace? Can it be greater than mine? If I come to the servant, do you disdain to come to the Lord? If I have received the baptism of the servant, do you disdain to be baptized by the Lord?
Source: Tractates on the Gospel of John (New Advent)