The wider context of Rev 19:12 is pretty spectacular (as is what follows to the end of the Book of Revelation)
Rev 19:11-18
11 I saw heaven standing open and there before me was a white horse, whose rider is called Faithful and True. With justice he judges and wages war. 12 His eyes are like blazing fire, and on his head are many crowns. He has a name written on him that no one knows but he himself.
13 He is dressed in a robe dipped in blood, and his name is the Word of God. 14 The armies of heaven were following him, riding on white horses and dressed in fine linen, white and clean. 15 Coming out of his mouth is a sharp sword with which to strike down the nations. “He will rule them with an iron scepter”
[Ps 2:9]. He treads the winepress of the fury of the wrath of God Almighty. 16 On his robe and on his thigh he has this name written:
King of Kings and Lord of Lords
17 And I saw an angel standing in the sun, who cried in a loud voice to all the birds flying in midair, “Come, gather together for the great supper of God, 18 so that you may eat the flesh of kings, generals and the mighty, of horses and their riders, and the flesh of all people, free and slave, great and small.”
The narrative continues through the next chapter where there is reference to the "first resurrection' of "the souls of those who had been beheaded because of their testimony about Jesus and *because of the word of God* " -
Rev 20:4-6
4 I saw thrones on which were seated those who had been given authority to judge. And I saw the souls of those who had been beheaded because of their testimony about Jesus and because of the word of God. They had not worshiped the beast or its image and had not received its mark on their foreheads or their hands. They came to life and reigned with Christ a thousand years. 5 (The rest of the dead did not come to life until the thousand years were ended.) This is the first resurrection. 6 Blessed and holy are those who share in the first resurrection. The second death has no power over them, but they will be priests of God and of Christ and will reign with him for a thousand years.
( even Satan gets a second chance in Rev: 20:7-9a : though for a second dispatching )
In Rev 20:12-15 the Book of Life features a couple of times (it's a feature of the Valentinian Gospel of Truth, at least)
Rev 20:12-15
11 Then I saw a great white throne and him who was seated on it. The earth and the heavens fled from his presence, and there was no place for them. 12 And I saw the dead, great and small, standing before the throne, and books were opened. Another book was opened, which is the book of life. The dead were judged according to what they had done as recorded in the books. 13 The sea gave up the dead that were in it, and death and Hades gave up the dead that were in them, and each person was judged according to what they had done. 14 Then death and Hades were thrown into the lake of fire. The lake of fire is the second death. 15 Anyone whose name was not found written in the book of life was thrown into the lake of fire.
Rev 21 starts
1 Then I saw “a new heaven and a new earth” [Isaiah 65:17], for the first heaven and the first earth had passed away, and there was no longer any sea. 2 I saw the Holy City, the new Jerusalem, coming down out of heaven from God, prepared as a bride beautifully dressed for her husband.
and ends
22 I did not see a temple in the city, because the Lord God Almighty and the Lamb are its temple. 23 The city does not need the sun or the moon to shine on it, for the glory of God gives it light, and the Lamb is its lamp. 24 The nations will walk by its light, and the kings of the earth will bring their splendor into it. 25 On no day will its gates ever be shut, for there will be no night there. 26 The glory and honor of the nations will be brought into it. 27 Nothing impure will ever enter it, nor will anyone who does what is shameful or deceitful, but only those whose names are written in the Lamb’s book of life.
In Revelation
23 John appears explicitly in the first person, as does Jesus
12 “Look, I [Jesus] am coming soon! My reward is with me, and I will give to each person according to what they have done. 13 I am the Alpha and the Omega, the First and the Last, the Beginning and the End.
14 “Blessed are those who wash their robes, that they may have the right to the tree of life and may go through the gates into the city.
15 "Outside are the dogs, those who practice magic arts, the sexually immoral, the murderers, the idolaters and everyone who loves and practices falsehood.
16 “I, Jesus, have sent my angel to give you [plural in the Greek] this testimony for the churches. I am the Root and the Offspring of David, and the bright Morning Star.”
Then John provides a final warning to anyone who adds or subtracts from a prophetic scroll
18 I warn everyone who hears the words of the prophecy of this scroll: If anyone adds anything to them, God will add to that person the plagues described in this scroll. 19 And if anyone takes words away from this scroll of prophecy, God will take away from that person any share in the tree of life and in the Holy City, which are described in this scroll.
nb. "the tree of life"