 Let me quote the late theologian John Stott, and the way, I think he explains this in a way that's just so clear. After God gave the promise to Abraham, he gave the law to Moses. Why? He had to make things worse before he could make them better. The law exposed sin, provoked sin, condemned sin, and the purpose of the law was to lift the lid off man's respectability and disclose what he really is underneath, sinful, rebellious, guilty, under the judgment of God, and helpless to save himself.