What?

First, in that it shows them that they cannot justify themselves by their works, it humbles them and disposes them to seek their salvation in Jesus Christ (Rom 3:3). Secondly, inasmuch as it requires of them much more than they are able to perform, it admonishes them to pray unto the Lord, that He may give them strength and power (Gal 4:6), and at the same time reminds them of their perpetual quilt, that they may not presume to be proud. Thirdly it is a kind of bridle, by which they are kept in the fear of God.