When we accept the Salvation offered by Jesus, we receive the Promise of Eternal life and our names are Written in the Book of Life. John 3:16
But it is possible for our name to be blotted out, if we fall into sin. Exodus 32:39, Psalms 69:28
Revelation 20:11-15, is plain: ONLY when the Book of Life is opened, will anyone receive immortality.
We become saved because our names have been written in the Book of Life from the foundation of the world. Our names are not written in the Lamb's Book of Life when we become saved. Our names are there before the foundation of the world.
Luke 10:20 (KJV) Notwithstanding in this rejoice not, that the spirits are subject unto you; but rather rejoice,
because your names are written in heaven.
Philippians 4:3 (KJV) 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.
Revelation 3:5 (KJV) 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 13:8 (KJV) 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 17:8 (KJV) 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.
There is more than one book in heaven from which the dead are judged. To be written among the book of the living is not the same as being written among the elect whose names are recorded in the Lamb's Book of Life from the foundation of the world.
Revelation 20:12 (KJV) 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.
There is both in heaven books that record the living, and there is also one book called the Lambs Book of Life. When one dies their names are blotted out of the books of the living, but when our names are written in the Lambs Book of Life they will never be blotted out.
Isaiah 4:3 (KJV) And it shall come to pass,
that he that is left in Zion, and
he that remaineth in Jerusalem, shall be called holy,
even every one that is written among the living in Jerusalem:
These two verses are not saying the righteous can be blotted out of the Lamb's Book of Life. The Lord tells Moses the one who sins against Him shall be blotted out of the book of the living, or that one shall die. Moses will not die nor be blotted out of the Lamb's Book of Life because he is righteous before God.
Exodus 32:32-33 (KJV) 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 in this Psalm David is praying that the LORD will destroy those who commit iniquity against him, so he asks God to not let them continue to live among the righteous, but rather blot them out from among the living, so their names are no longer recorded among those living in righteousness.
Psalm 69:27-29 (KJV) Add iniquity unto their iniquity: and
let them not come into thy righteousness. Let them be blotted out of the book of the living, and not be written with the righteous. But I
am poor and sorrowful: let thy salvation, O God, set me up on high.
When the Book of Life is opened at the GWTJ the righteous have already received immortal and incorruptible bodies of flesh. Because the physical bodies of all who have ever lived will be resurrected to stand before God at Judgment Day. But when all who have done good are bodily resurrected on the last day of this age, they will also be changed from mortal to immortal and corruptible to incorruptible. But for those resurrected who have done evil, they will be physically resurrected to be judged by what is written in the books, and since they are "the dead" they will not be found written in the Book of Life, and therefore they will be cast into the eternal flames.
John 5:24 (KJV) Verily, verily, I say unto you,
He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life.
John 5:28-29 (KJV) Marvel not at this: for
the hour is coming, in the which all that are in the graves shall hear his voice, And shall come forth; they that have done good, unto the resurrection of life; and they that have done evil, unto the resurrection of damnation.
While the dead bodies of all who in life remained spiritually dead are resurrected to damnation, the dead bodies of all who have done good are resurrected and changed into incorruptible and immortal bodies of flesh to live with Christ forever on the new earth.
1 Corinthians 15:52-53 (KJV) In a moment, in the twinkling of an eye,
at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible,
and we shall be changed. For this corruptible must put on incorruption, and this mortal must put on immortality.
So whose names are written in the Lamb's Book of Life from the foundation of the world? According to the Word of God "
whosoever believes", all who are born again, born from above, born of the Spirit of Christ while alive in this age are the elect of God, and have no fear of the second death, that is the Lake of Fire. And when Christ returns the second time, believers clothed in immortal and incorruptible bodies of flesh will be re-united with our eternal spirits that Christ brings back with Him when He comes again from heaven.
1 Thessalonians 4:14 (KJV) For if we believe that Jesus died and rose again, even so
them also which sleep in Jesus will God bring with him.