Just before leaving for heaven, He commanded them to baptize each new convert. 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. It is a gesture symbolizing our desire to die with Jesus, leaving behind us the old man , that is, our former life of sin, and thereafter walking 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. Therefore, if anyone is in Christ, he is a new creation.
Baptism symbolizes the replacement of the old man by the new man.
Likewise you also, reckon yourselves to be dead indeed to sin, but alive to God in Christ Jesus our Lord. The longsuffering of God waited in the days of Noah, while the ark was being prepared, in which a few, that is, eight souls, were saved through water. There is also an antitype which now saves us, namely baptism. This is the answer of a good conscience toward God , the public demonstration of our faith in Jesus Christ. Baptism is, in a sense, the marriage of the believer with his Savior Jesus Christ.