baptisma

This noun names one particular ceremony, not washing in general. It was a new word. Greek already had ordinary words for dipping and for ritual washing, but this exact form was, as far as we can tell, first used by Christians (and possibly by John's followers) to name one specific rite. Even when the historian Josephus described John, he reached for a different word (βαπτισμός); the New Testament keeps this one for the baptism John began and the church carried on.

Within that rite the New Testament uses the word two ways. It covers John's baptism, a one-time washing tied to repentance and the coming judgment, and it covers Christian baptism, the initiation of a believer into Christ and his people. The same noun serves both, so what tells them apart is the surrounding words and the setting, never the noun by itself.

The New Testament writers load this rite with deep meaning:

• being buried and raised with Christ
• being made one body
• an appeal to God from a clear conscience

But that meaning comes from what they say about baptism, not from the shape of the word. Reading later church arguments back into the bare word is a common mistake.

When Jesus asks whether his followers can be baptized with the baptism he faces, and says he has a baptism still to undergo, he is not talking about the water rite. He is drawing on the older, everyday meaning of the related verb (βαπτίζω), which pictured something plunged under, sunk, or swamped, the way a ship goes down or a person is drowning in debt.

His coming death is pictured as a great flood closing over him, echoing the Old Testament image of the faithful sufferer sinking in the waters of judgment. This is the same picture Paul later uses when he says believers are baptized into Christ's death: to be baptized into him is to be brought inside that flood and carried through it.