A metaphor used by John the Baptist. John was looking for someone who would “baptize...with the Holy Spirit and with fire” (Matthew 3:11; Luke 3:16). In this context, fire means judgment, which would purify those who repent (compare Isaiah 4:4; Malachi 3:2–3) and destroy those who do not (Malachi 4:1; Matthew 3:10, 12).
The prophets and writers of apocalyptic texts often talked about a time of trouble and suffering needed before the new age could come. They called this time “the messianic woes,” “the birth pangs of the Messiah,” “a river of fire.” Similar ideas to John’s can be found in Isaiah 30:27–28 and in the non-biblical text 2 Esdras 13:10–11. John the Baptist likely used these ideas and expressed them through his act of baptism. His phrase “baptize in fire” probably meant the purifying judgment that would bring about the new age and bring people into it.
The Bible does not mention baptism of fire again. The gospels of Mark and John shorten John the Baptist’s preaching and leave out any mention of judgment. After Pentecost, when the Holy Spirit came to Jesus's followers, John's water baptism is seen as fulfilled in baptism in the Holy Spirit. However, Jesus seemed to share John's belief in a fiery purification (Mark 9:49). He referred to his own death as a baptism and likely included this fire (Luke 12:49–50). Jesus’s death is seen as enduring the fiery baptism for others.
Paul the apostle also speaks of baptism into Christ as a baptism into Christ’s death (Romans 6:3). Thus, John’s idea of a purifying baptism of fire for those who repent is most closely fulfilled when believers unite with Christ in his death and share in his sufferings. Only then can they fully share in Christ’s risen glory (Romans 6:5; 8:17–23; Philippians 3:10–11).