ROMANS 7:8 Verse 8 continues to explicate the relation between the law and sin with reference to the fall of Adam. Indeed v 8 amounts in effect to a description of the tactics of the serpent, here personified as "sin." Sin (the serpent) was lurking in the garden prior to man's fall, but had found no opportunity to attack man until the commandment, "You shall not eat of it" (Gen 2:17) had been given. It was precisely through this commandment, by using this commandment, that sin was able to tempt Adam and to produce in him the primary sin of lust. What thus begins to become clear is the nature of the law's agency in all this. The real culprit is sin as a power for evil quite distinct from the law, but taking advantage of the law, perverting the function of the law so that the same commandment ceases to make man conscious that selfish desire is lust and instead provokes the very desire it was designed to warn against. Sin uses the commandment intended as a check on man's inquisitiveness actually to stimulate that inquisitiveness, to transform inquisitiveness into acquisitiveness. All this is the work of sin; the power which provokes man's selfish grasping in all its forms was already active at the beginning, and still dominates the old epoch.
from page 400, Word Biblical Commentary on Romans