Tonight I began reading James D.G. Dunn’s collection of essays in The Christ and the Spirit: v. 2: Pneumatology. In his 1978 “Spirit and Holy Spirit in the New Testament” he discusses John’s baptism as it relates to the “birthpangs of the messiah” and he says this of John’s baptism (p. 6):
“John’s baptism in the Jordan (presumably by immersion) was therefore a very potent symbol of the end-time tribulation = baptism in Spirit and fire = God’s fiery pneuma like a great stream through which all humanity must pass. Those who acknowledged their liability to judgment by submitting to the symbolized judgment of John’s baptism would experience the messianic woes as a cleansing by a spirit of judgment and by a spirit of burning (Isa. 4:4). Those who denied their guilt and did not repent would experience the Coming One’s baptism in Spirit and fire as the bonfire which burned up the unfruitful branches and chaff.”
While I know ritual cleansing such as dipping in a mikveh provided a symbolism of washing could it be that John’s baptism (and subsequently later Christian baptism?) presented participants with an additional symbol: that of being made wet to resist the coming flame? John’s message was (1) be baptized in water unto repentance and (2) one is coming who baptizes with spirit/wind and fire. Dunn’s wording suggest that those who were not “dampened” (if you will) by his baptism unto repentance would be annihilated by the coming spirit/wind and fire, but those who had been dampened would find it to be a purifying and purging flame.
This may be simplistic, but it would present John’s message as easily understood by the crowds as this sort of symbolism is imaginable, even tactile.