Now some Pharisees who had been sent questioned him, “Why then do you baptize if you are not the Christ, nor Elijah, nor the Prophet?”
Baptism was used by the Jews to admit Gentile converts. The males were circumcised but both males and females were baptized, denoting the ceremonial removable of the contaminants they had acquired in the Gentile world. However baptism of Jews was unheard of. Gentiles needed cleansing, of course, but Jews were God’s people and to put them into the same class as Gentiles would have been horrifying. However, some people thought that baptism would come with the advent of the Messiah. Eze 36:25, Zech 13:1
Ezekiel 36:25 I will sprinkle clean water on you, and you will be clean; I will cleanse you from all your impurities and from all your idols.
Zechariah 13:1 “On that day a fountain will be opened to the house of David and the inhabitants of Jerusalem, to cleanse them from sin and impurity.