Christians are "salt", but that salt can become tasteless and worthless (Matt 5:13). Hebrews 6:4-6 echoes this notion, that those who believe, if they then fall away, are doomed. Rev 3:5 warns that the Messiah can obliterate names from the Book of Life. CONCLUSION: It seems that, although the elect have been written into the Book of Life since Creation, even still, now, in this life, they can "fumble the ball" and be "cut from the Team." That is, you can start as a member of "the Messiah's crew", but lose your election through falling away in this life. In that sense, election is a "negative sum game". I know of no Scripture that says names can be added to the Book of Life, but it is clear that names can be removed. Crudely, I sense a parallel with Eden — man started in Grace, but then Fell away. You start at 100.00%, but then satan assaults you and hacks you down, you buckle from the pressure, and are cut from the Team.