I have need to be baptized by thee. It is certain, that John acknowledged Christ to be not only a distinguished prophet, as many foolishly dream, but the Son of God, as he really was: for otherwise he would have dishonored God by lowering his holy calling to a mortal man. How he came to know this, the reader will learn by consulting John's Gospel, (1:15,33.) There was, no doubt, plausibility in this ground of refusal, that Christ had no need of his baptism: but John was mistaken in not considering, that it was for the sake of others that baptism was asked. [1] And so Christ bids him consider, what was suitable to the character of a servant, (Philippians 2:7,) which he had undertaken; for a voluntary subjection takes nothing from his glory. Though the good man [2] remained ignorant, for a time, of some part of his public duty, this particular error did not prevent him from discharging, in a proper and lawful manner, his office of Baptist. This example shows, that we do not act rashly, in undertaking the commission which the Lord has given us, according to the light we enjoy, though we do not immediately comprehend all that belongs to our calling, or that depends upon it. We must also observe his modesty, in giving up his opinion, and immediately obeying Christ.

Footnotes

1 - "Que c'est pour le profit des autres, et non pas pour le sien, que Christ demande d'estre baptize." -- "That it is for the benefit of others, and not for his own, that Christ asks to be baptized."

2 - "Quelque excellent personnage qu'il fust." -- "However excellent a person he was."

John forbade him - Refused him.
I have need - It is more suitable that I should be baptized with thy baptism, the Holy Spirit, than that thou shouldest be baptized in water by me. I am a sinner, and unworthy to administer this to the Messiah.

John forbad him - Earnestly and pressingly opposed him: this is the proper import of the words διεκωλευεν αυτον. I have observed that δια, in composition, most frequently, if not always, strengthens the signification in classic authors. - Wakefield.

But John forbad him, saying,.... It appears from hence, that John knew Christ before he baptized him, and before he saw the Spirit descending and abiding on him, John 1:33 wherefore that was not a signal, whereby he should first know him but whereby his knowledge of him should be confirmed; which knowledge of him he had, not through his kindred to him, or by any conversation he had with him before, but by immediate, divine revelation: upon which account he "forbad him"; refused to administer the ordinance to him; earnestly entreated that he would not insist upon it; desired to be excused being concerned herein: and this he did, partly lest the people should think Christ was not so great a person as he had represented him to be; yea, that he was one of the penitent sinners John had admitted to his baptism; and chiefly because of the majesty and dignity of Christ's person, who he knew stood in no need of such an outward ordinance; and because of his own unworthiness to administer it to him, as is evident from what follows,
I have need to be baptized of thee; not with water baptism, which Christ never administered, but with the baptism of the Spirit, which was his peculiar office. Hence we learn, that though John was so holy a man, was filled with the Holy Ghost from his mother's womb, had such large measures of grace, and lived such an exemplary life and conversation; yet was far from thinking, that he was perfect and righteous in himself, but stood in need of Christ, and of more grace from him. He seems surprised that Christ should come to him, and make such a motion to him; when it was his duty and privilege to come to him daily for fresh supplies of grace, and always to trust in him for life and salvation;
and comest thou to me? who am of the earth, earthly, when thou art the Lord from heaven; "to me", a poor sinful creature, when thou art the Holy One of God; "to me", who am thy servant, when thou art Lord of all; "to me", who always stand in need of thy grace, when thou art God all sufficient.

But John forbade him--rather, "was (in the act of) hindering him," or "attempting to hinder him."
saying, I have need to be baptized of thee, and comest thou to me?--(How John came to recognize Him, when he says he knew Him not, see John 1:31-34). The emphasis of this most remarkable speech lies all in the pronouns: "What! Shall the Master come for baptism to the servant--the sinless Saviour to a sinner?" That thus much is in the Baptist's words will be clearly seen if it be observed that he evidently regarded Jesus as Himself needing no purification but rather qualified to impart it to those who did. And do not all his other testimonies to Christ fully bear out this sense of the words? But it were a pity if, in the glory of this testimony to Christ, we should miss the beautiful spirit in which it was borne--"Lord, must I baptize Thee? Can I bring myself to do such a thing?"--reminding us of Peter's exclamation at the supper table, "Lord, dost Thou wash my feet?" while it has nothing of the false humility and presumption which dictated Peter's next speech. "Thou shall never wash my feet" (John 13:6, John 13:8).

John forbade him. The objection that John made to the baptism of Christ implies some knowledge of him. Their mothers were cousins, but there is no evidence that Jesus and John had ever met. The Spirit had told John to proclaim the Redeemer and had given him a sign by which he should know him. When Jesus came before him, he perhaps knew, by the Spirit, his purity, and may have believed that he was the Messiah, but as yet he "knew him not" (see John 1:33). He could not be certain until he saw the divine sign.
I have need to be baptized of thee. These words were uttered under the conviction, not certainty, that Jesus was the Christ.