There are a number of references I'd like you to look at:
first reference
Acts 19:1 And it happened, while Apollos was at Corinth, that Paul, having passed through the upper regions, came to Ephesus. And finding some disciples 2 he said to them, “Did you receive the Holy Spirit when you believed?”
So they said to him, “We have not so much as heard whether there is a Holy Spirit.”
3 And he said to them, “Into what then were you baptized?”
So they said, “Into John’s baptism.”
4 Then Paul said, “John indeed baptized with a baptism of repentance, saying to the people that they should believe on Him who would come after him, that is, on Christ Jesus.”
5 When they heard this, they were baptized in the name of the Lord Jesus. 6 And when Paul had laid hands on them, the Holy Spirit came upon them, and they spoke with tongues and prophesied. 7 Now the men were about twelve in all.
Notice - Paul is speaking with disciples - (saved) -
1. They are already had experienced the baptism into repentance -
2. Then Paul Baptized them a second time in the Name of the Lord Jesus and the Holy Spirit came upon them.
Second reference -
Heb 6:1 Therefore, leaving the discussion of the elementary principles of Christ, let us go on to perfection, not laying again the foundation of repentance from dead works and of faith toward God, of the doctrine of baptisms, of laying on of hands, of resurrection of the dead, and of eternal judgment.
Baptisms - plural.
Third reference:
John 20:21 21 So Jesus said to them again, “Peace to you! As the Father has sent Me, I also send you.” 22 And when He had said this, He breathed on them, and said to them, “Receive the Holy Spirit.
They received the Holy Spirit - then later -
Acts 1: 4 And being assembled together with them, He commanded them not to depart from Jerusalem, but to wait for the Promise of the Father, “which,” He said, “you have heard from Me; 5 for John truly baptized with water, but you shall be baptized with the Holy Spirit not many days from now.”
Three distinct and very plainly written Scriptures - each demonstrating more than one Baptism.
look again at
Eph 4:4 There is one body and one Spirit, just as you were called in one hope of your calling; 5 one Lord, one faith, one baptism; 6 one God and Father of all, who is above all, and through all, and in you all.
Is it possible that the subject of the sentence is our entrance into the Body of Christ and yes, there is one Baptism into Christ - but as evidenced by Paul's own writings and actions - there was another where the Holy Spirit was involved.
If your answer is no - them please explain the above notated Scriptures.