"Now the serpent was more subtil than any beast of the field which the LORD GOD had made. And he said unto the woman, Yea, hath God said, Ye shall not eat of every tree of the garden?" (Genesis 3:1)
The first entrance of sin into the world was Satan's subtle suggestion to Eve that God's word might not be true and authoritative after all. Then came Satan's blatant "Ye shall not surely die" (v. 4), openly charging the Creator with falsehood. Ever since that time, the basic root of every sin has been unbelief--the implicit denial of the Creator's Word.
Therefore, God's judgment on human sin will be in relation to His Word. Jesus said: "There is one that accuseth you, even Moses, in whom ye trust. For had ye believed Moses, ye would have believed me" (John 5:45-46). He also said: "He that rejecteth me, and receiveth not my words, hath one that judgeth him: the word that I have spoken, the same shall judge him in the last day" (John 12:48). In principle, the Lord Jesus tells us that both Old Testament ("the law of Moses") and New Testament ("the law of Christ") will be witnesses against us at God's judgment throne.
In fact, at the final judgment, the "books" are specifically said to be the basis of God's condemnation of the unsaved: "And I saw the dead, small and great, stand before God; and the books were opened . . . and the dead were judged out of those things which were written in the books, according to their works" (Revelation 20:12). These books surely include the books of the Bible, wherein are written the laws of God, against which men and women are to be judged. Since even one transgression makes one guilty (James 2:10), none could ever stand at the judgment by his own works. But since unbelief is the essence of sin, faith in God's Word, and in the person and work of the Savior revealed in God's Word, brings forgiveness, salvation, and righteousness. HMM