Romans 7:8

Sin, taking occasion. Sin, or concupiscence, which is called sin, because it is from sin, and leads to sin, which was asleep before, was awakened by the prohibition; the law not being the cause thereof, nor properly giving occasion to it: but occasion being taken by our corrupt nature to resist the commandment laid upon us. (Challoner) --- Sin. The apostle here calls concupiscence by the name of sin; because it is the consequence and punishment of it, and drags us along to sin. This takes occasion from the precept of the law to induce us to transgress it; for we are naturally inclined to do what is forbidden. --- Nitmur in vetitum --- which is the offspring of a disorderly love of liberty and independence. Without the law sin was dead, because concupiscence had nothing to rouse and trouble it. It was like a torrent which rolled rapidly, without resistance in its channel, but as soon as the law came and put an obstacle, it began to spread itself far and wide, and commit the strangest ravages. Or it may be explained thus: without the law sin was dead; not being known to the world, and not imputed to us as a transgression. He speaks here of the transgressions of the written law, not the law of nature, of which each one has a sufficient knowledge to render him inexcusable, whenever he transgresses it. (Calmet) --- Without the law sin was dead; that is, many sins were so little known, that before the written law they seemed no sins; not but that, at all times, reason and conscience shewed many things to be sinful and ill done, so that whosoever acted against these lights could not be excused. See what St. Paul says of the heathen philosophers, chap. i. (Witham)