For the law was given through Moses; grace and truth came through Jesus Christ. (John 1:17, ESV)Through Moses came the Law. And through that Law came our understanding of our own sinfulness. As Paul tells us in Romans 3:19-20, "...through the law comes knowledge of sin." The deeper problem mentioned in that same passage is that nobody is justified (declared righteous) by keeping the law. The Law doesn't solve our problem, it only serves to make us more aware of our problem, we are deeply, inherently, sinful.
But through Jesus Christ, the full revelation of God, we are recipients of grace (unmerited favor) and truth (comprehension of reality).