Lawful use of the Law

What shall we say then? Is the law sin? God forbid. Nay, I had not known sin, but by the law: for I had not known lust, except the law had said, Thou shalt not covet.
Romans 7:7 

"The first of all lawful use of the law is to bring people to Christ,

that they may be justified by faith.
That is the object of it,—to give the knowledge of sin, and to bring people to Christ, that they may be justified by faith."

A.T. Jones