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” (Revelation 13:8). 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.
So how then does the record of our lives contained in “the books” have a part in our judgment? The answer is that the books contain enough evidence of our belonging to Christ that they function as a public confirmation of our faith and our union with him.
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 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.
Then God will open the books and will use the record of sin to glorify his Son’s supreme sacrifice, and he use the last page to show the change that was wrought in the thief’s attitudes and words. That last page — the last hours on the cross — will be the public confirmation of the thief’s faith and union with Christ.
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 change that shows the reality of faith — the reality of regeneration and union with Christ. That is how I enter the day, confident that my condemnation is past (Romans 8:3), and that my name is in the book of life, and that the one who began a good work in me will bring it to completion at the day of Christ.