Paul understood his main calling was to preach the Gospel by which men are saved, and the baptism of water was not about that. There was a debate about those who wanted water baptism, even though it was not necessary, and they decided it should not be forbidden, which is why Paul baptised those he did.
Acts 10:47 Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we?
But, as Dan pointed out, water baptism was being phased out. It wasn't part of Paul's Gospel. Because of Paul's preaching, people realised the ONE BAPTISM that mattered was the baptism of the Spirit into the body of Christ.
Probably some were and some weren't....just like today, but water baptism is not necessary for salvation.
I would suggest to you that water baptism is part of the gospel. Please bare with me.
John the baptist was to "prepare" the way of the Lord. He did so by baptizing, Mk. 1:1-4. This was something new. In the OT, there were washings but not baptisms. The OT was a physical shadow to help us better understand the spiritual things in Christ. In this case, the high priest could only approach God after washing with water and offering blood (animal). I would suggest to you we approach God the same way today but by better things, the water of baptism and the blood of Christ.
Johns baptism was for repentance but could not remove sin because it didn't have Jesus' blood behind it. Once Jesus offered himself in true holy of holies, he was given
ALL authority in heaven and on earth, Matt. 28:18. He then commissions his apostles to "make" Christians by baptizing them
in the name of the father, son and HS. I would suggest to you that is the key, "
in the name of".
Here is a clear example of that, Acts 18:24-19:7. In Ephesus Apollos preached Jesus. The bible tells us:
He was an eloquent man, competent in the Scriptures. 25 He had been instructed in the way of the Lord. And being fervent in spirit, he spoke and taught accurately the things concerning Jesus, though he knew only the baptism of John. He knew the truth with only one exception, baptism.
When Paul comes in to town behind him, he asks the people if they received the Holy Spirit
when they believed. If Paul knows the HS baptizes upon belief, it doesn't make sense for him to ask this question. He isn't questioning their belief, remember they had been taught accurately Jesus.
They tell him they didn't know there was a HS. Notice Paul's next question.
3 And he said, "Into what then were you baptized?"
When he finds out it was Johns baptism, he says that was for repentance and was looking forward to Christ (preparing the way). After that was cleared up, Paul baptized them again
in the name of Jesus.
I would suggest to you being baptized
in the name of Jesus is how we call upon his name and access his blood. Remember, that is how
Jesus said to make Christians of
all nations and
every creature. When we believe and are baptized, we can now approach God because we have the water and the blood just like the example of the high priest. Jn. 3:5
Jesus answered, "Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God.
I would suggest 1 Cor. 12:13 is used to support a falsehood. I would go into it but this is long enough already.