The most important fact in anyone’s life, whether they acknowlege it or not, is to have their name written in Heaven:
“Nevertheless do not rejoice in this, that the spirits are subject to you, but rather rejoice because your names are written in heaven.” (Luke 10:20 NKJV)
Where it is written in Heaven, the Old Testament refers to it as the book. The New Testament calls it the Lamb’s book of life or the book of life. You must have your name written in it in order to enter Heaven. The only way to have your name written in it is by accepting Jesus Christ as your LORD and Savior. Once you have it written there, you must make sure, until your race is finished on this earth, it is never blotted out.
The book of life is referred to in the singular. All those whose names are written in it will spend eternity with Jesus in the New Heaven, New Earth, and New Jerusalem.
Whereas when the plural books is referred to it is where those destined for eternity in the Lake of Fire will be judged out of according to their works. This will determine the severity of their punishment for eternity.
The following Scriptures give us the insight we need:
Yet now, if thou wilt forgive their sin–; and if not, blot me, I pray thee, out of thy book which thou hast written.
And the LORD said unto Moses, Whosoever hath sinned against me, him will I blot out of my book.
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.
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.
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.
The beast that thou sawest was, and is not; and shall ascend out of the bottomless pit, and go into perdition: and they that dwell on the earth shall wonder, whose names were not written in the book of life from the foundation of the world, when they behold the beast that was, and is not, and yet is.
And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works.
A fiery stream issued and came forth from before him: thousand thousands ministered unto him, and ten thousand times ten thousand stood before him: the judgment was set, and the books were opened.
And whosoever was not found written in the book of life was cast into the lake of fire.
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.
And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book.
In conclusion, I have added a PDF below that points out that the Book of Life and the Lamb’s Book of Life are one in the same: