Thematic Bible: Why the law was given

So then, as the effect of one act of wrongdoing was that punishment came on all men, even so the effect of one act of righteousness was righteousness of life for all men. Because, as numbers of men became sinners through the wrongdoing of one man, even so will great numbers get righteousness through the keeping of the word of God by one man. And the law came in addition, to make wrongdoing worse; but where there was much sin, there was much more grace: read more.
That, as sin had power in death, so grace might have power through righteousness to eternal life through Jesus Christ our Lord.