The word “repentance” means “to change one’s mind.” In essence, John the Baptist was calling upon the Jewish people to repent or change their minds about which Judaism they were going to follow: pharisaic Judaism or biblical Judaism.
Those who were willing to make the commitment and follow biblical Judaism would undergo water baptism to show their new identification with John’s kingdom message. This message was based upon biblical Judaism, the only Judaism that would qualify the people for Messiah’s kingdom.
