John came baptising in the wilderness and preaching a baptism of repentance for the remission (forgiveness) of sins. Mark 1:4

Or do you not know that as many of us as were baptised into Christ Jesus were baptised into His death? Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life. For if we have been united together in the likeness of His death, certainly we also shall be in the likeness of His resurrection, knowing this, that our old man was crucified with Him, that the body of sin might be done away with, that we should no longer be slaves of sin. Romans 6:3–6