"Now the law came in to increase the trespass, but where sin increased, grace abounded all the more." Romans 5:20
"The Law came in as a sort of 'afterthought,' a secondary and subordinate stage, in the Divine plan, causing the indefinite multiplication of sins which, like the lapse or fall of Adam, were breaches of express command. Multiplied indeed they were, but only with the result of calling forth a still more abundant stream of pardoning grace."
Paraphrase of Romans 5:20 in Sanday and Headlam, Romans (ICC), page 139.