John 1:25 - Matthew Poole's English Annotations on the Holy Bible

The Pharisees themselves would allow the Messiah, or Elias, or a prophet, to make any additions to or alterations in the worship of God, but none else: hence it is they ask, by what authority he baptized, if he were none of these? From whence we may learn, that although they might have some umbrage of that baptismal washing which was under the gospel, to commence into a sacrament, or federal sign, in the washing of their proselytes, or of Jewish children when they were circumcised; yet John's action was looked upon as new, who baptized adult Jews: now the care of the sanhedrim was to keep the worship of God incorrupt, and the Pharisees amongst them had a particular zeal in the case, especially so far as the traditions of the elders were concerned.