First off there is no water cult, it is what the Bible and history teaches.
When John the Baptist was baptizing for the remission of sins, it was not the water that washed away sins, it was the event. Christ understood what it meant.
Christian baptism is where the concept of a born again Christian comes from. Baptism does not forgive sins it gives the believer a new beginning. Sin is a double edged sword, not only is it a transgression against the will of God but the person knows the nasty things they did....as long as they exist Satan can come back and accuse you of them…..
So it is also a matter of reconciling that within themselves. They can get forgiveness from Christ but they still did it. Baptism provides a new start ....and new person....the sins are gone because the person is gone. A new person in Christ.
Part of the confusion is Acts 2:38 itself.....Peter said to them, “Repent, and each of you be baptized in the name of Jesus Christ for the forgiveness of your sins; and you will receive the gift of the Holy Spirit ....Some take this that Baptism forgives sins but actually it is the whole process. But still the words say it. It is just the way it is worded….it is Christ that provides the power behind the physical act of baptism. John the Baptist baptized for the remission of sins and the Jews came to Christ asking where did John the Baptist get that authority….it was not John, it was God.
The person that come out of that water is a new person in Christ. The person that went down dies in Christ and the person that comes up has a clean slate.
Romans 6:3-4 Or don’t you know that all of us who were baptized into Christ Jesus were baptized into his death? 4 We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life.
It is not really forgiveness of sins as far as Christ is concerned that person and their sins never happened. From that point on our sins are between us and Christ.