was the Gentile inclusion contingency? if it is, does it not then give room for Open-Theism?
If not, how to prove Gentile inclusion as elect in the OT?
1) With respect to "contingency," the Bible is full of examples of series of eventualities that are cause-and-effect; a series of which would have been different and have a different conclusion if other human decisions had been made along the way. The free decisions of men are part of the fixed and eternal predestinating decree of God, so that what is contingent in the earthly realm is not contingent from God's foreordination of all things.
2) Having said that, Gentile inclusion is by no means "contingency," in the sense that God first makes an attempt to get the physical seed of Abraham to accept his blessing; and because they refuse him he then retools his plans and pursues the "Gentile option." As Gal.3:8 plainly states, referencing Gen.12:3, so goes Paul's argument: that "Gentile inclusion" belongs to the first issuance of the Promise to Abraham, it isn't an afterthought, and it even stands as the ultimate goal of the Promise, as expressed. We might even say that from the first word God intends to bless the whole earth through the nation of Israel. The biggest apparent "contingency" is that he works around the chosen people's persistent refusal to obey him to that end, which goal he achieves while using their very refusal as the means to saving not only the Gentiles, but the Jews as well.
Further, if election is conceived
primarily in a corporate and indistinct way, and in such a way as God may select and then deselect the same entity,
contingent upon the presence or absence of faithfulness (even if he then later reselects the same, again with faithfulness as basis)--all this tends to undermine salvation (election) by grace alone, apart from works. Personal election is effectively removed from the discussion of individual salvation, other than once again having a vague, "backstory,"
pro nobis (for us) feel to it. What's missing is the specific "for me!" aspect.
Corporate election, if it is to have any real analogy to personal salvation, must have constituent individual election. Think of a satellite image of earth. Corporate-electionists would have us conceive of election as a "clear" picture of earth from a million miles away, but the resolution is low; no increase in focus will render particulars with greater clarity, and in fact will distort the picture. To them, this is the design. Personal-election is a high-resolution picture; there's one view that takes in the big picture, and a zoom feature that takes one in close, so that individual features of the whole are themselves revealed as highly detailed microcosms within the big picture. God doesn't merely choose the big-picture, and leave the self-choosers to fill in the "minor collage elements" on his big canvas.
Corporate election is basically meaningless, without individual election. God chooses Abraham's seed, but that election ends up being an election of One Person. Paul points to individuals as being elect (or reprobate), as proof of his comfortable doctrine for believers (discomforting for the faithless). He writes that not all
individuals deserve the name "Israel" who have some claim to membership in
corporate Israel.
Finally, consider texts such as Ps.87:4-6 & Is.56:3, 6-8.