Many people wonder about 'the book of life': When is one's name written in it? Can one's name be blotted out? Do we have eternal security?
The idea of the book of life is firmly grounded in the Old Testament. In Nehemiah 7:4 we read about the genealogical record of the first Jews that returned to Israel after the exile. Some people's names were recorded during the Persian period (Nehemiah 12:22-23).
We see that record keeping has always been a part of God's ways. Remember the books at the judgment (Daniel 7:10c; Revelation 20:12). Books are part of God's precision; nobody will ever be able to accuse God of being unfair.
When is one's name written in the book of life?
That is a very difficult question, since we are never told precisely when. God, who knows the beginning and the end, knows whose names are there. We do not know, for the simple reason that it might cause us to let go of our zeal, expectancy of the second coming, and labour of love for the Lord. However, in Malachi 3:16 we read: 'A scroll of remembrance was written in His presence concerning those who feared the Lord and honored His name.' Combined with Philippians 4:3 it seems as if it has to do with being busy with the Lord's business: 'I ask you ...to help these women who have contended at my side in the cause of the gospel, along with Clement and the rest of my fellow-workers, whose names are in the book of life.' This also accords with Jesus who said: 'He who overcomes will, like them, be dressed in white. I will never blot out his name from the book of life...' (Revelation 3:5). We surmise that those who accepted Jesus, love the Lord, and are busy doing His will ('This is love for God: to obey His commands' 1 John 5:3), will have their names in the book.
Can names be erased?
We must also accept that the book is continually updated. In Ezekiel 18:21-24 the teaching is very clear: if an unrighteous man turns to God and obeys, he will live (his name will be written in the book of life). If a righteous man turns away from God, he will die (his name will be blotted out of the book of life). This must have been the case with Demas. He worked with Paul (name in book), then deserted Paul because he loved the world (2 Timothy 4:9). Those who love the world cannot please God (1 John 2:15-17), and his name must have been deleted. Jesus is very clear: not he who begins, but he who finishes is the one who overcomes (Revelation 3:5, 21:7).
Is there any security for the believer?
Yes, in doing God's will and living in a relationship with Him. That person's name cannot be blotted out of the book of life. That person's life will be characterized by zeal for the Lord, love for the Lord, and doing what He wants. Any person who relies on being part of the covenant family, who believes that belonging to a church safeguards him, who relies on election, who is lazy, who is more interested in the world than God, and who takes no steps to keep the relationship alive, has reason to fear. His name might not be in the book on the day of judgment. Taking chances might work in other places, but with God the failure rate is 100%. God is too precise and meticulous: nobody will ever be able to accuse Him of favoring those who don't deserve it. His grace and mercy is unlimited, but if a person doesn't make use of it by obeying God, he is on a very slippery path.
For a person who has faith in God and acts on it, there is nothing to fear: his name will be written in the book of life. Those who rely on isolated scriptures and the dogma of a church, will have a day of crying and gnashing of teeth, and Jesus will be unable to help. He can help now to set one's life in order. This side of the grave, God's grace and mercy is unlimited. Don't abuse it, act on it.