All who dwell on the earth will worship him, everyone whose name has not been written from the foundation of the world in the book of life of the Lamb who has been slain. — Revelation 13:8

All the names of God's chosen people were written in a book.

When?

From the foundation of the world. This book has been around since the foundation of the world.

What is this book?

It is the book of life of the Lamb who has been slain. Which means God had planned a sacrifice for the redemption of His people since before the fall, from the foundation of the world. And this is exactly what we find in the book of Acts.

“Men of Israel, listen to these words: Jesus the Nazarene, a man attested to you by God with miracles and wonders and signs which God performed through Him in your midst, just as you yourselves know⁠— this Man, delivered over by the predetermined plan and foreknowledge of God, you nailed to a cross by the hands of godless men and put Him to death. But God raised Him up again, putting an end to the agony of death, since it was impossible for Him to be held in its power. — Acts 2:22-24

Jesus Christ was delivered over to be nailed to a cross by the predetermined plan of God. Redemption was planned out before the fall ever happened, even from the foundation of the world.

Not only that, but before the foundation of the world His elect people were chosen for salvation.

just as He chose us in Him before the foundation of the world, that we would be holy and blameless before Him. In love — Ephesians 1:4

The counsel of the Lord stands forever, The plans of His heart from generation to generation. — Psalm 33:11

The Lord of hosts has sworn saying, “Surely, just as I have intended so it has happened, and just as I have planned so it will stand, to break Assyria in My land, and I will trample him on My mountains. Then his yoke will be removed from them and his burden removed from their shoulder. This is the plan devised against the whole earth; and this is the hand that is stretched out against all the nations. For the Lord of hosts has planned, and who can frustrate it? And as for His stretched-out hand, who can turn it back?” — Isaiah 14:24-27

“Remember the former things long past, For I am God, and there is no other; I am God, and there is no one like Me, Declaring the end from the beginning, And from ancient times things which have not been done, Saying, ‘My purpose will be established, And I will accomplish all My good pleasure’; Calling a bird of prey from the east, The man of My purpose from a far country. Truly I have spoken; truly I will bring it to pass. I have planned it, surely I will do it. — Isaiah 46:9-11

Why did His purpose include a fall?

Israel has been saved by the Lord With an everlasting salvation; You will not be put to shame or humiliated To all eternity. For thus says the Lord, who created the heavens (He is the God who formed the earth and made it, He established it and did not create it a waste place, but formed it to be inhabited), “I am the Lord, and there is none else. “I have not spoken in secret, In some dark land; I did not say to the offspring of Jacob, ‘Seek Me in a waste place’; I, the Lord, speak righteousness, Declaring things that are upright. “Gather yourselves and come; Draw near together, you fugitives of the nations; They have no knowledge, Who carry about their wooden idol And pray to a god who cannot save. “Declare and set forth your case; Indeed, let them consult together. Who has announced this from of old? Who has long since declared it? Is it not I, the Lord? And there is no other God besides Me, A righteous God and a Savior; There is none except Me. “Turn to Me and be saved, all the ends of the earth; For I am God, and there is no other. “I have sworn by Myself, The word has gone forth from My mouth in righteousness And will not turn back, That to Me every knee will bow, every tongue will swear allegiance. “They will say of Me, ‘Only in the Lord are righteousness and strength.’ Men will come to Him, And all who were angry at Him will be put to shame. “In the Lord all the offspring of Israel Will be justified and will glory.” — Isaiah 45:17-25