A: In ancient times, cities would register their citizens in a book until their death; then their names were marked out of the book of the living. The Book of Life seems to be a corresponding Heavenly practice whereby the names of those who possess eternal life and are therefore citizens of Heaven are written in the Book of Life. The practice emphasizes the security of a persons eternal destiny - because Jesus states that the names shall never be blotted out of the Book of Life - cp. Revelation 3:5. The failure to have one's name written in the Book of Life results in eternal condemnation - cp. Revelation 20:15. At the end of time, when God judges the righteous, the summary is that only those whose names are written in the Lamb's Book of Life are permitted to enter the New Jerusalem (the eternal state for the believer).
References to the book of life in the OT seem to be transitional - from
the practices of ancient cities to a reference to those who are among the
people of God on earth. The fully developed analogy leading to the Lamb's
Book of Life is the final stage. Thus, the OT references to the book of
life do not refer to the eternal state of believers, but merely to the
physical life of God's people while still on earth - cp. Exodus 32:32-33;
Psalm 69:28; Isaiah 4:3. To confuse these references with the New Testament
references will cause confusion. Again, the emphasis in the New Testament
on a Heavenly Book of Life is on the assurance that nothing will separate
us from the Love of Christ - cp. Romans 8:38-39.