Found Written in the Book of Life or Cast into the Lake of Fire

If anyone was not found having been written in the Book of Life, he was cast into the lake of fire. (Revelation 20:15) 

Revelation 20:15 "means that the only criterion of salvation is to have one's name written in the Book of Life" (David E. Aune, Revelation 17-22, 1103). For those whose names are not written in the Book of Life, only their "works"–written in the other books–can testify for them (Rev 20:12-13), and since all our works fall short of God's holy standard, those works are insufficient to save (at best), or they serve to justly call for our greater condemnation.

Notice the passive verbal forms in Revelation 20:15. Divine action is directly implied. God is sovereign over the names written in the Book of Life and over whom is cast into the lake of fire. All who are saved from the lake of fire owe their salvation to God, and they have no grounds for boasting before Him.