Matthew Henry Commentary Romans 6:3-10

"Or are ye ignorant that all we who were baptized into Christ Jesus were baptized into his death? We were buried therefore with him through baptism unto death: that like as Christ was raised from the dead through the glory of the Father, so we also might walk in newness of life. For if we have become united with [him] in the likeness of his death, we shall be also [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, that so we should no longer be in bondage to sin; for he that hath died is justified from sin. But if we died with Christ, we believe that we shall also live with him; knowing that Christ being raised from the dead dieth no more; death no more hath dominion over him. For the death that he died, he died unto sin once: but the life that he liveth, he liveth unto God." — Romans 6:3-10 (ASV)

Baptism teaches the necessity of dying to sin, and being, so to speak, 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 to sin and a new birth to righteousness, but they never passed from the family of Satan to that of God.

The corrupt nature (called the 'old man' because it is 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 still 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 with, so that the believer may no longer be the slave of sin, but live to God and find happiness in His service.