Three possibilities exist in terms of reconciling Revelation 13:8 with open theism.
1) First, the “from the foundation of the world” clause can attach to either “everyone whose names have not been written” or to “the lamb that was slain.” For example, the TNIV translates this passage “All inhabitants of the earth will worship the beast—all whose names have not been written in the Lamb’s book of life, the Lamb who was slain from the creation of the world. ” So it is with many translations of this passage. If this is correct, the passage suggests that the crucifixion of Christ was part of Gods’ plan from the beginning, but not that people’s names were or were not written in “the book of life” from the foundation of the world.
2) The phrase “from the foundation” (apo kataboleis) can mean “from before” or “from the time of” (=since). So even if we attach the phrase to “everyone whose name has not been written…” the passage need only refer to those who didn’t enter into eternal life from the beginning of the world – that is, throughout history. As history progresses, God (metaphorically of course) puts into his “book of life” all people who enter into a life-giving relationship with him.
3) Several times in Scripture God warns people that he may blot their names out of the book of life (Exod. 32:33; Rev. 3:5, cf. Rev. 22:18). In this light, it seems we should not think that having one’s name in or out of “the book of life” is a permanent thing. On a side note, if names were written (or not written?) in the book of life before the world began, and if one can’t add or detract from this book, one might legitimately wonder what these passages mean.
Applied to the foreknowledge debate, if God foreknew from all eternity that certain names would be “blotted out” of his book, one has to wonder why God bothered to put them there in the first place? If God may indeed “take away [a]… person’s share in the tree of life and in the holy city” (Rev. 22:19), and God knew this would happen, why did he give them a share in the first place? If names can be added and/or deleted from the book of life, it suggests that the eternal destiny of these people was not fixed in God’s mind (=in “the book”) from the start .