# for repentance
"to show that you have repented"
# he who comes after me
John was speaking about the Christ, although he probably did not know who that was.
# is mightier than I
"is more important than I am"
# He will baptize you with the Holy Spirit and with fire
This means John's baptism only symbolically cleanses people of their sins. The baptism by Holy Spirit and fire will truly cleanse people of their sins. If possible, use the word "baptize" in your translation to keep the comparison to John's baptism.