Bede the Venerable — as excerpted in the Catena Aurea on Mark 1:4-8

“(in Marc. i. 2) It is evident that John not only preached, but also gave to some the baptism of repentance; but he could not give baptism for the remission of sinsc. For remission of sins is only given to us by the baptism of Christ. It is therefore only said, Preaching the baptism of repentance for the remission of sins; for he preached a baptism which could remit sins, since he could not give it. Wherefore as he was the forerunner of the Incarnate Word of the Father, by the word of his preaching, so by his baptism, which could not remit sins, he preceded that baptism, of penitence, by which sins are remitted.”