The meaning of water baptism has never changed from it's first use by John the Baptist: John did baptize in the wilderness, and preach the baptism of repentance unto the remission of sins. (Mk.1:4)
And then by Jesus:
John 3:22-26 (New International Version)
22After this, Jesus and his disciples went out into the Judean countryside, where he spent some time with them, and baptized. 23Now John also was baptizing at Aenon near Salim, because there was plenty of water, and people were constantly coming to be baptized. 24(This was before John was put in prison.) 25An argument developed between some of John's disciples and a certain Jew[a] over the matter of ceremonial washing. 26They came to John and said to him, "Rabbi, that man who was with you on the other side of the Jordanthe one you testified aboutwell, he is baptizing, and everyone is going to him."
John 4:1-2 (New International Version)
1The Pharisees heard that Jesus was gaining and baptizing more disciples than John, 2although in fact it was not Jesus who baptized, but his disciples.
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On Pentecost, everyone who was a follower of John the Baptist, had to get re-baptized into the name of Jesus in order to show that they were now followers of Him. However, everyone who was water baptized by Jesus (or any of His disciples) did not have to be re-baptized.
According to the doctrine of 'water baptism salvation' everyone who had been water baptized by Jesus, or any of His disciples, would have had to have been re-baptized because there was no church, or body (physical or spiritual) for those converts to have been baptized into, before that Pentecost morning.