The believing sinner is baptized (placed) into the Body of Christ by the Holy Spirit
(I Corinthians 12:13)
The Holy Spirit has established the unity within the Body
of Christ, which includes the one baptism associated with the one body (Ephesians 4:3-5)
The believer's baptisminto the Body of Christ identifies the believer with the death and resurrectionof Christ(Romans 6:3-5)
Israel's dry passage through the Red Sea is called a baptism
(I Corinthians 10:1-2) - it identified them with Moses who descended into the sea (death)
and ascended out of it (resurrection)«Exodus 14:26-30»
Water baptism was NOT part of Paul's gospel preaching (I Corinthians 1:17 cf. Romans 3:25),
BUT it was certainly part of Peter's
gospel preaching (Acts 2:38)
John preached the "baptism of repentance" for
the "remission of sins" (Mark 1:4)
The theme of the kingdom message to Israel was "repent
and be baptized" (Matthew 3:1-2,5-6)
Israel's hope was to be a "kingdom of priests"
(Exodus 19:6),
a "royal priesthood" (I Peter 2:9)
The purpose of John's baptizing with water was to introduce
Israel's "Priest King" (John 1:30-31 cf. Zechariah 6:12-13) Who would "sprinkle clean water" upon her (Ezekiel 36:24-25)