Luke 315 The people were waiting expectantly and were all wondering in their hearts if John might possibly be the Messiah. 16 John answered them all, “I baptize you with[b] water. But one who is more powerful than I will come, the straps of whose sandals I am not worthy to untie. He will baptize you with[c] the Holy Spirit and fire. 17 His winnowing fork is in his hand to clear his threshing floor and to gather the wheat into his barn, but he will burn up the chaff with unquenchable fire.” 18 And with many other words John exhorted the people and proclaimed the good news to them.The Lord said He would baptize us with Holy Spirit AND fire! In Luke 17 it is stateed that this person "will burn up the chaff with unquenchable fire.' " So, what then do you think the fire part of "Holy Spirit and fire" means?
Since the word "and" connects the word on the left to the word on the right, both come not just the Holy Spirit. Because of V17 I believe that the fire represents a falling away of all the useless stuff in our lives, in other words, everything that would keep us from our relationship with Jesus Christ.
So you wonder why God always requires character development and letting go of the past things or getting rid of things you don't need. That is why!
And I think it's neat that John used the word "unquenchable" which alludes to the fact that Jesus/God is a jealous God and is jealous of EVERYTHING that takes you away from Him.