What were the Jews doing in John's baptism?
The Jews were repenting of their failure of the system of Law and everything else, showing saving faith that the King and Kingdom was present. Through John's baptism of repentance, they prepared their hearts and minds for the King and His Kingdom, unable to separate repentance from that baptism.
Les explains that John maintained that if they were going to show saving faith in the fact that the King and the Kingdom is here, they would have to show that with the baptism of repentance. That's why it's always called the baptism of repentance, and the two could not be separated. As these Jews were repenting of their failure of the system of Law and everything else, they were now preparing their hearts and minds for the King and His Kingdom. Les also notes the division among believers over baptism, but the Scripture shows John's baptism was specifically a baptism of repentance for Israel.