Thomas Aquinas

“ I answer that, Two things may be considered in the baptism of John---namely, the rite of baptism and the effect of baptism. The rite of baptism was not from men, but from God, who by an interior revelation of the Holy Ghost sent John to baptize. But the effect of that baptism was from man, because it effected nothing that man could not accomplish. Wherefore it was not from God alone, except in as far as God works in man.
Reply to Objection 1: By the baptism of the New Law men are baptized inwardly by the Holy Ghost, and this is accomplished by God alone. ”

“ Now, it belongs of necessity to Christ's baptism that it be given not only in water, but also in the Holy Ghost, according to Jn. 3:5: "Unless a man be born of water and the Holy Ghost, he cannot enter into the kingdom of God." Wherefore in the case of those who had been baptized with John's baptism in water only, not merely had the omission to be supplied by giving them the Holy Ghost by the imposition of hands, but they had to be baptized wholly anew "in water and the Holy Ghost." ”

“ As Augustine says (Contra Faust. xix) , our sacraments are signs of present grace, whereas the sacraments of the Old Law were signs of future grace. Wherefore the very fact that John baptized in the name of one who was to come, shows that he did not give the baptism of Christ, which is a sacrament of the New Law. ”