7 But the Lord Jesus Christ could, if He wished, have given power to one of His servants to give a baptism of his own, as it were, in His stead, and have transferred from Himself the power of baptizing, and assigned it to one of His servants, and have given the same power to the baptism transferred to the servant as it had when bestowed by the Lord. This He would not do, in order that the hope of the baptized might be in him by whom they acknowledged themselves to have been baptized.
He would not, therefore, that the servant should place his hope in the servant. And therefore the apostle exclaimed, when he saw men wishing to place their hope in himself, “Was Paul crucified for you? Or were ye baptized in the name of Paul?” Paul then baptized as a servant, not as the power itself; but the Lord baptized as the power. Give heed. He was both able to give this power to His servants, and unwilling. For if He had given this power to His servants— that is to say, that what belonged to the Lord should be theirs— there would have been as many baptisms as servants; so that, as we speak of the baptism of John, we should also have spoken of the baptism of Peter, the baptism of Paul, the baptism of James, the baptism of Thomas, of Matthew, of Bartholomew: for we spoke of that baptism as that of John.
But perhaps some one objects, and says, Prove to us that that baptism was called the baptism of John. I will prove it from the very words of the Truth Himself, when He asked the Jews, “The baptism of John, whence was it? From heaven, or of men?” Therefore, lest as many baptisms should be spoken of as there are servants who received power from the Lord to baptize, the Lord kept to Himself the power of baptizing, and gave to His servants the ministry. The servant says that he baptizes; he says so rightly, as the apostle says, “And I baptized also the household of Stephanas;” but as a servant.
Therefore, if even he be bad, and he happen to have the ministration of baptism, and if men do not know him, but God knows him, God, who has kept the power to Himself, permits baptism to be administered through him.
Source: Tractates on the Gospel of John (New Advent)