Baptism teaches the necessity of dying to sin, and being as it were buried from all ungodly and unholy pursuits, and of rising to walk with God in newness of life. Unholy professors may have had the outward sign of a death unto sin, and a new birth unto righteousness, but they never passed from the family of Satan to that of God.
The corrupt nature, called the old man, because derived from our first father Adam, is crucified with Christ, in every true believer, by the grace derived from the cross. It is weakened and in a dying state, though it yet struggles for life, and even for victory.
But the whole body of sin, whatever is not according to the holy law of God, must be done away, so that the believer may no more be the slave of sin, but live to God, and find happiness in his service.