“And another book was opened, which is
 the book of life.” Revelation 20:12 

The names of the elect are written in the book of life. 
They do not obtain salvation by chance, but were 
elected by God to eternal life and happiness before 
the foundation of the world. Now their names being 
once written in the book of life, they shall never, 
never be blotted out of that book! In the book of 
predestination there is not one blot to be found;
the salvation of the elect is most sure and certain!

“I will never blot out his name from the
book of life
.” Revelation 3:5

The book of life is the book of all those who were
elected and redeemed to life, through Jesus Christ.
This book of life contains a register of such particular
persons in whose salvation, God from all eternity
determined to have His mercy glorified; and for whom 
merited faith, repentance, and perseverance—
that they should repent, believe, and be finally saved.

“The book of life shall be opened;” that is to say, the
decrees of God will be then published and made known,
which now are sealed up in His bosom and locked up
in His archives. Then it will be seen whom are appointed
to eternal life—for the glorifying of God’s free, rich, and
sovereign grace; and whom He purposed to leave in
their sins, and to perish forever—for the exaltation of
His justice.

“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.”
Revelation 21:27 

The book of life shall be opened in the great day, 
because then it shall be shown . . .
  who were elect—and who were reprobates;
  who truly believed in Christ—and who did not;
  who worshiped God in spirit and in truth—and who did not;
  who walked with God as Noah did—and who did not;
  who truly reverenced God—and who did not;
  who followed the Lamb wherever He went—and who did not;
  who were sincere—and who were not;
  who are sheep—and who are goats;
  who are sons of God—and who are slaves of Satan;
  who have mourned for their sins—and who have made a sport of sin;
  who preferred Christ above ten thousand worlds—and who did not;
who preferred their farms, and their oxen, and their swine,
yes, their very lusts—before a Savior, a Redeemer!

“If anyone’s name was not found written in the book of life,
he was thrown into the lake of fire!” Revelation 20:15