6 Since, then, John had accepted a baptism which may be properly called the baptism of John, but the Lord Jesus Christ would not give His baptism to any, not that no one should be baptized with the baptism of the Lord, but that the Lord Himself should always baptize: that was done, that the Lord should baptize by means of servants; that is to say, those whom the servants of the Lord were to baptize, the Lord baptized, not they. For it is one thing to baptize in the capacity of a servant, another thing to baptize with power. For baptism derives its character from Him through whose power it is given; not from him through whose ministry it is given. As was John, so was his baptism: the righteous baptism of a righteous man; but of a man who had received from the Lord that grace, and so great grace, that he was worthy to be the forerunner of the Judge, and to point Him out with the finger, and to fulfill the saying of that prophecy: “The voice of one crying in the wilderness, Prepare ye the way for the Lord.” As was the Lord, such was His baptism: the baptism of the Lord, then, was divine, because the Lord was God.
Source: Tractates on the Gospel of John (New Advent)