This verse explains the penalty for not being in the Lamb's book of life, which immediately should rise within us the desire to look into the word of God as to how we should have our names written in the Lamb's book of life in order to escape the lake of fire.

When searching the Scriptures, there are many verses that include the book of life, but interestingly the way to enter into the book of life is not laid out in the verses where "book of life" is mentioned. However, we can see what happens when our name is in the book of life, and see the similarities and attempt to discern how to have our names written in the Lamb's book of life.

And I intreat thee also, true yokefellow, help those women which laboured with me in the gospel, with Clement also, and [with] other my fellowlabourers, whose names [are] in the book of life. (Philippians 4:3) In this passage, the ones whose names are written in the book of life labor with those who preach the gospel of Christ.

He that overcometh, the same shall be clothed in white raiment; and I will not blot out his name out of the book of life, but I will confess his name before my Father, and before his angels. (Revelation 3:5) This passage clearly states of those written in the book of life have overcome sin and wear the clothing of righteousness, as described in Revelation 19:8.

And all that dwell upon the earth shall worship him, whose names are not written in the book of life of the Lamb slain from the foundation of the world. (Revelation 13:8) This verse tells us of those who worship the beast do not have their names written in the book of life, which allows us to conclude that those whose names are written in the book of life worship the Lamb of God rather than the beast.

And there shall in no wise enter into it any thing that defileth, neither [whatsoever] worketh abomination, or [maketh] a lie: but they which are written in the Lamb's book of life. (Revelation 21:27) Here this passage is describing New Jerusalem, and those who defile or are abominable are not inside; but it also says people who are written in the book of life dwell in New Jerusalem. In Revelation 21:3-4, the Bible tells us in New Jerusalem, "there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain," which the believer can experience as well once entered into the Kingdom of God. Jesus also says in John 3:5 that no man can enter the Kingdom of Heaven unless he is born again. Acording to 1 Peter 1:3, the way to be born again is through faith in the physical resurrection of Jesus Christ from the dead.

In order to be written in the Lamb’s Book of Life, according to the previous verses, a person needs to be born again through faith in the physical resurrection of Jesus Christ, which allows access into the Kingdom of Heaven in Spirit while awaiting the coming of the Lord Jesus Christ; the person needs to worship Jesus Christ as the one true God, which is how to worship God in Spirit and in truth, because the truth of Jesus Christ is His Divinity and mercy while suffering for us at the cross of Calvary, while maintaining His Godhead despite His sufferings; a person needs to stop sinning and actually appropriate the promses of God to fulfill all righteousness by beliving His blood shed on the cross of Calvary is good enough to wash away all our sins, defeating sin and death at the foot of the cross, laying down His life for our behalf, taking upon Himself the wrath of God so we may escape His wrath and be reconciled to Him for faith and glorying in Jesus Christ for all time forever, and abstaining from the lusts and filth of the flesh in all honesty, sincerity, and godliness, knowing His blood is powerful enough to deliver us from all unrighteousness as the Bible explicitly commands us in various places (1 John 1:7, Romans 6:1-7, etc); and the person must preach the Gospel of Jesus Christ to all men, women, and children in all places all over the world.

In a nutshell, for those who need a clear statement: be born again by believing Jesus Christ rose physically from the dead; worship Jesus Christ as the one true God; stop sinning by believing Jesus’s blood shed ont he cross is powerful enough to free you from all known sin; and preach the gospel to anyone you can reach. If you do these things, you will be written in the Lamb’s Book of Life. Remember, if it wasn’t for God doing it through His Son, you wouldn’t have a way to enter into life in the first place, so give God all the glory, honor, and praise for His mercy upon such a poor, worthless sinner such as I! In Jesus’ name, Amen!