One might think baptism in water ends when Jesus takes over. For John says,
“I have baptized you with water, but he will baptize you with the Holy Spirit” (Mark 1:8).
Yet, after talking with Nicodemus, Jesus goes on doing as John does.
After this Jesus and his disciples went into the Judean countryside, and he remained there with them and was baptizing. John also was baptizing at Aenon near Salim, because water was plentiful there, and people were coming and being baptized.…[Some report to John,] “Rabbi, he who was with you across the Jordan, to whom you bore witness—look, he is baptizing, and all are going to him” (John 3:22-23,26).
Now both are using water. Jesus soon has His followers dipping even more people than John’s growing number (John 4:1-2). With each new person baptized, John and Jesus prove that water is important. All of this is at the very time when Jesus requires the new birth of water and the Spirit. How can Nicodemus fail to see which “water” is required?
The common people can see well enough. So many respond that reports state in a general way: “All the people were baptized” (Luke 3:21). Only a few – mainly leaders of religion – see no importance in baptism. They reject the authority behind it (Luke 20:1-8).
When all the people heard this, and the tax collectors too, they declared God just, having been baptized with the baptism of John, but the Pharisees and the lawyers rejected the purpose of God for themselves, not having been baptized by him (Luke 7:29-30).