This refers to the same people who came to John. This could be translated as "because the people."
## I baptize you with water ##
"I baptize using water" or "I baptize by means of water"
## not worthy even to untie the strap of his sandals ##
This could be translated as "not important enough even to loosen the straps of his sandals." Untying the straps of sandals was a duty of a slave. John was saying that the one who would come is so great that John was not even worthy enough to be his slave.
This metaphor compares literal baptism that brings a person into contact with water to a spiritual baptism that brings them into contact with the Holy Spirit and with fire. (See: [[rc://en/ta/man/translate/figs-metaphor]])
## fire ##
Here this refers to God's power. (See: [[rc://en/ta/man/translate/figs-metaphor]])