The specific mention of fire likely has two purposes. For one it draws attention to times where God has revealed himself in the past in or with fire (Exodus 3:2; Exodus 14:24; Exodus 19:18; 1 Kings 18:38–39; 1 Kings 18:38–39). For another, it connects with what John the Baptist said about Jesus, that Jesus would be the one who baptizes with the Holy Spirit and fire
(Luke 3:16). The coming of the Holy Spirit at Pentecost is thus a fulfillment of John’s prophecy.1 In this regard we must remember that for John, fire was a means of judgment and cleansing.2
3 And divided tongues as of fire appeared to them and rested on each one of them.