Note 5 at Lu 3:16: Only Luke and Matthew mentioned this fire in association with the baptism of the Holy Ghost. It isn't made clear in Scripture what this fire is, but from the fact that in both Matthew and Luke, mention of this fire is followed by statements of the Lord burning up the chaff with unquenchable fire, it's possibly speaking of judgment. Some have referred to it as a fire for purifying (Mal 3:2-3). Another possibility is that it was prophetic of the "cloven tongues like as of fire" that appeared at the outpouring of the Holy Ghost on the Day of Pentecost (Ac 2:3).