What does John 1:31 mean?

Given that the mothers of Jesus and John the Baptist were relatives (Luke 1:35–36, 39–41), it may seem odd for John to say he didn't recognize Jesus as Messiah at first. He had simply been baptizing, so that Christ would be revealed to Israel (Malachi 3:1). Although the Baptist and Jesus were related, and the Baptist had responded to the presence of Jesus while in the womb, they probably hadn't spent much time around each other. One was raised in Nazareth, the other near Jerusalem.

Since Jesus hadn't yet performed any miracles, it's reasonable to think that the Baptist didn't know Jesus was the Messiah until seeing the vision of the dove (John 1:32). This is part of the mystery of Jesus' youth: the Bible doesn't give many details about Jesus prior to the start of His ministry.

The word used for "baptism" is the Greek baptizō, which literally means "to immerse," but with a specific spiritual context. John's purpose in calling people to repentance, demonstrated by baptism, was to open the path of understanding for Jesus. Once Christ appeared on the stage, it was time for the Baptist to step aside.