Revelation 3:5

He that overcometh, the same shall be clothed in white raiment; he that overcometh in the spiritual fight, shall be honoured as a triumpher. And I will not blot out his name out of the book of life; that is, I will give him everlasting life: the phrase is an allusion to men who use to keep books, and in them the names of persons to whom they will show kindness. The book of life; applied to God, signifieth his eternal predestination, or purpose to bring some to heaven; out of which book, though none can be blotted out whose name is once wrote in, yet those whose names are in this book may be under some fears and apprehensions to the contrary. Christ assures them to the contrary, that they shall certainly be saved, but lets them know that this assurance depends upon their perseverance; of which also some make this phrase a promise. But I will confess his name before my Father, and before his angels; in the day of judgment I will own them, and acknowledge them as mine before my Father and all the angels, Matthew 10:32 Luke 12:8.