The "book" mentioned in Daniel 12:1 probably refers to the Book of Life earlier mentioned in Exodus 32 as a registry of persons of God's faithful saints. The Book of Life is a registry of all those born from above, officially registered in the kingdom of Heaven: all the faithful men and women in the Old Testament, Paul's contemporaries in the New Testament, those glorified at the first resurrection, and those glorified at the Great White Throne Judgment. The common denominator of all these groups seems to be overcoming and faithfulness, those whose sins have been forgiven.