Our old man. — “Our old self” (Vaughan), as in Ephesians 4:22; Ephesians 4:24; Colossians 3:9-10.
The old self, or that congeries of evil habits acquired in the state of heathenism, was, ideally if not actually, mortified and killed in our baptism. This change was wrought by a power brought to bear upon the will through the contemplation of the crucifixion of Christ. Hence, instead of saying simply “mortified,” the Apostle writes rather “crucified,” i.e. put to death, not in any way, but specially through the cross.
That the body of sin might be destroyed. — The “body of sin” is the body subject to sin, or that supplies sin with the material on which it works. This substratum of carnal and fleshly desire, the Apostle tells us, is to be ascetically chastened and disciplined until it ceases to be a source of sin.