Matthew 3:11
I indeed baptize you in water for repentance, but he who comes after me is mightier than I, whose shoes I am not worthy to carry. He will baptize you in the Holy Spirit (some version add: and with fire).
Luke 3:16:
John answered them all, “I indeed baptize you with water, but he comes who is mightier than I, the latchet of whose sandals I am not worthy to loosen. He will baptize you in the Holy Spirit and fire.
Matthew and Luke add fire and a bit of Wrath of God to the cooler John the Baptist in Mark. Personally, I don’t think the Matthew & Luke versions add anything. The point is surely to be baptised in the Holy Spirit; the rest is just decoration.
Mark might not be a “passionate” read, but I like the cool simplicity and directness of the message.
For trainspotters: at Biblos.com all Greek texts for the Luke include the “and fire” (“και πυρι”), and for the Matthew all but one has it, the “Greek NT: Byzantine / Majority Text (2000).” So the Majority Text is in the minority. I found some explanation of what the Majority Text is here (I didn’t read it all because I am not a trainspotter ;).
To an unknown God 