What does John 1:25 mean?

Prior to the public ministries of John the Baptist and Jesus, baptism was already practiced in the region as a symbol of repentance. The Greek term is baptizō, which literally means "immersion." Converts to Judaism were sometimes baptized, so the interrogators (John 1:19–24) were already aware of what it meant. However, to the Pharisees, there was little reason for someone who was already a Jew to be baptized. In their minds, a person who was going to baptize others ought to hold priestly office or have prophetic authority.

But John the Baptist says he is not the long-awaited Messiah. He is not Elijah, who many believed would come back to life to tell others about the Promised One. Nor is he the prophet whom Moses promised (Deuteronomy 18:18). The Baptist hasn't made any claims to authority. In fact, he's made it plain that his mission is to make a path for someone else (John 1:23; Malachi 3:1). Since the investigators were out of ideas, they resorted to essentially asking John the Baptist, "Who do you think you are?"

As was his pattern, the Baptist will ignore questions about himself, and focus once again on the Messiah.