God is Holy and a part of that Holiness is revealed to us in the fact that God is a just judge (One before whom we must all stand to give an account of our lives - Romans 14:12). Once we discover exactly what God requires of us in the law we respond in one of two ways - hardened defiance or broken contrition.
It is a horrible cruelty to preach the law (God's requirements) without following it with the gospel. (God's solution to our inability to meet His requirements). The reason so many Christians find their religion to be a burden that they drag through life is because they are hearing all law and no gospel. The following clip illustrates the point perfectly.