This significance of baptism - the dying or drowning of sin - is not fulfilled completely in this life. Indeed this does not happen until man passes through bodily death and completely decays to dust. As we can plainly see, the sacrament or sign of baptism is quickly over. But the spiritual baptism, the drowning of sin, which it signifies, lasts as long as we live and is completed only in death. Then it is that a person is completely sunk in baptism, and that which baptism signifies comes to pass.
Therefore this whole life is nothing else than a spiritual baptism which does not cease till death, and he who is baptized is condemned to die. It is as if the priest, when he baptizes, were to say, 'Lo, you are sinful flesh. Therefore I drown you in God's name and in his name comdemn you to death, so that with you all your sin may die and be destroyed.' Wherefore St. Paul, in Romans 6[:4], says, 'We were buried with Christ by baptism into death.' The sooner a person dies after baptism, the sooner is his baptism completed. For sin never ceases entirely while the body lives, which is so wholly conceived in sin that sin is its very nature, as the prophet says [Ps. 51: 5], 'Behold I was conceived in sin, and in iniquity did my mother bear me.' There is no help for the sinful nature unless it dies and is destroyed with all its sin. Therefore the life of a Christian, from baptism to the grave, is nothing else than the beginning of a blessed death. For at the Last Day God will make him altogether new." Luther's Works, American Ed. Vol. 35, pp. 30, 31.