This is a very tough chapter, luckily it is not the last chapter.
Revelation 20:15 Gill
And whosoever was not found written in the book of life,…. Upon the opening of it, Rev 20:12 as all that worship the beast, and wonder after him, Rev 13:8 and all wicked men, everyone of them:
was cast into the lake of fire; where are the devil, beast, and false prophet, Rev 19:20. It is a saying of R. Isaac (m),
“woe to the wicked, who are not written בפתקא, “in the book”, for they shall perish in hell for ever and ever:”
and in the Targum on Eze 13:9 it is said of the false prophets,
“that בכתב חיי עלמא, “in the writing of eternal life” (or in the book of eternal life), which is written for the righteous of the house of Israel, they shall not be written.”
There seems to be some allusion in the phrase used here, and in the preceding verse, and elsewhere in this book, to the lake Asphaltites, a sulphurous lake, where Sodom and Gomorrah stood, which the Jews call the salt sea, or the bituminous lake; and whatsoever was useless, or rejected, or abominable, or accursed, they used to say, to show their rejection and detestation of it, let it be cast into the sea of salt, or the bituminous lake; thus, for instance,
“any vessels that had on them the image of the sun, or of the moon, or of a dragon, יוליכם לים המלח, “let them cast them into the salt sea”, or bituminous lake (n).”
(m) Tosaphta in Zohar in Gen. fol. 78. 2. (n) T. Bab. Avoda Zara, fol. 42. 2. Vid. ib. fol. 49. 1. &. 53. 1. & 71. 2. & Nazir, fol. 24. 2. & 26. 1, 2. Bava Metzia, fol. 52. 2. Temura, fol. 22. 2. & Meila, fol. 9. 2. & 10. 1.