All who dwell on earth will worship [the beast], everyone whose name has not been written before the foundation of the world in the book of life of the Lamb who was slain. (Revelation 13:8)
Salvation is secured for all who are written in the book of life.
The reason that being written in the book of life secures our salvation is that the book is called “the book of life of the Lamb who was slain.” The names in this book are not saved on the basis of their deeds. They are saved on the basis of Christ’s being slain.
But John says in Revelation 20:12, “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.” So, how then does the record of our lives contained in “the books” have a part in our judgment, if we are saved on the basis of Christ being slain?
The answer is that the books, which record our deeds, contain enough evidence of our belonging to Christ that they function as a public confirmation of our faith and our union with Christ.
Consider Revelation 21:27: “Nothing unclean will ever enter [the New Jerusalem], nor anyone who does what is detestable or false, but only those who are written in the Lamb’s book of life.” Here the result of being written in the “book of life” is not only not perishing, but also not practicing detestable, sinful behaviors.
For example, consider the thief on the cross. Jesus said that he would enter paradise (Luke 23:43). But what will judgment be like for him when the books are opened? More than 99.9% of his life will be sin.
His salvation will be secured by the blood of Christ. His name will be in the book of life of the Lamb that was slain.
Then God will open the books. First, he will use the lifelong record of sin to glorify his Son’s supreme sacrifice. And, second, God will read that last page, where the thief’s dramatic transformation on the cross is recorded. This work of God in his life, recorded in the books, about that last day will be the public confirmation of the thief’s faith and union with Christ. And Christ will be the basis of his salvation, not his works.
Therefore, when I say that what is written in the books is a public confirmation of our faith and of union with Christ, I do not mean that the record will contain more good works than bad works.
I mean that there will be recorded there the kind of life in Christ that shows the reality of faith — the reality of regeneration and union with Christ. That is how we enter each day as a Christian: confident that our condemnation is past (Romans 8:1), and that our name is in the book of life, and that the one who began a good work in us will bring it to completion at the day of Christ.