Revelation 17

The beast that you saw was, and is not, and will ascend out of the bottomless pit and go to perdition. And those who dwell on the earth will marvel, whose names are not written in the Book of Life from the foundation of the world, when they see the beast that was, and is not, and yet is. v.8

Read chapter 17
In this chapter we read of a woman sitting on a scarlet beast. She seems to symbolize a city of riches and wealth. Her name written on her head is:
MYSTERY, BABYLON THE GREAT,
THE MOTHER OF HARLOTS
AND OF THE ABOMINATIONS
OF THE EARTH
so blatant and obvious of her whoredom yet she even causes John to marvel at her. The angel asks why he marvels and tells him that those that marvel at her are not written in the Book of Life. What exactly is the Book of Life? Bible teacher Nathan C. Johnson describes it as "that the Book of Life is a book in which God alone may write the names of all who are His. One’s name may be blotted out from there as well as written there, yet again it is only God Who has the right to either write or blot out a name from this Book. The final fate of all men when it comes to resurrection to life or else to the lake of fire is in God’s hands, and this is symbolized by the Book of Life. Whether this is really a book, or whether it is some other kind of record that we cannot understand, or whether it is merely something in the mind of God, the reality of it is that God’s choice is what determines whether or not someone has Life who is raised at the Great White Throne, or at any other time, for that matter" (www.precepts.wordpress.com).

Us as believers today are sealed with the Holy Spirit and therefore written in the Book of life. Yet let us not marvel at obvious sins that can entrance us. What easily entrances you away from godly focus?