John himself provides the answer in his next words: “according to what they had done.” Those deeds were recorded in God’s registers, described as “the books.” God had created people to exercise dominion over his world (Genesis 1:26–27) and would reward people according to how they handled that mandate (Genesis 2:17). So the Preacher had taught that “God will bring every deed into judgment, with every secret thing, whether good or evil” (Ecclesiastes 12:14; see further Matthew 12:36; Romans 14:12). God’s judgment will not be impulsive or whimsical but will be perfectly fair, based strictly on facts, namely, an accurate record of actual conduct in response to the mandate given at creation.
12 And I saw the dead, great and small, standing before the throne, and books were opened. Then another book was opened, which is the book of life. And the dead were judged by what was written in the books, according to what they had done.