But sin, taking occasion by the commandment, wrought in me all manner of concupiscence... For sin, taking occasion by the commandment, deceived me, and by it slew me.–Romans 7:8, 11
The law is just, holy and good, but very dangerous to creatures such as us. We are sinners by nature and would sin without the law. But such is the rebellion of our flesh that when the law is brought to bear on us, we do not sin less, but more. It aggravates our natural rebellion, and propels us on an ever-increasing course of sin. The fault lies not in the law, but in us; for it is the sin already present in us that produces this deadly result.
But sin, taking advantage of the opportunity afforded by the commandment goes even farther to bring death, for it not only aggravates our moral rebellion, but also deceives us. Now, how can sin deceive me through the law and thus kill me? Does sin make me think the law says it is all right to covet, blaspheme, etc.? No, sin (our sinful nature) deceives us by making us think we can gain God's blessings by our efforts in the law. The law teaches us that we are sinners. But sin deceives us into thinking we can keep the law and thus be righteous. This effectively shuts us off from the way of God's grace and thereby, we are slain.
So the law is found to be the catalyst of a double death in those who come under its jurisdiction. They are propelled both to corruption and self-righteousness, both of which are sure courses to eternal death.