How do we know a believer's name is written in the Lamb's Book of Life?

The assurance of having one’s name written in the Lamb's Book of Life comes from the promise of salvation through faith in Jesus Christ. When a person believes in Christ and accepts His sacrifice, they are adopted into God's family and granted eternal life. This is affirmed in verses like Ephesians 1:4-5, where it speaks of being chosen in Christ before the foundation of the world. A true believer's identity is thus secured in the grace of God, highlighting that the assurance lies not in personal merit, but solely in the redemptive work of Christ, which ensures that their name is recorded for eternity.