It makes sense, except that you have to explain how that relates to the gentiles place in the tree. Israel is spoken of as a single entity, while the gentiles are addressed on an individual basis. And that's where the potential for confusion and misunderstanding comes in.
I don't disagree that Israel in Romans 11 is the sum total of Israel—the nation of Israel. And that the promises made to the Patriarchs on behalf of their descendants will never be revoked from the nation as a whole. The key here being, different Israeli branches are grafted back in where Israeli branches were broken off. And so there is nothing irrevocable at all about the promises of God to those individual branches that were previously broken off because of unbelief. The gift and calling were indeed revoked from them personally! They will never walk in what they could have walked in while they were alive in the nation of Israel. But the gift and calling have not been revoked from the nation as a whole. Future Israelis will indeed walk in the gift and calling of God despite the fact that so many did not. Paul uses himself as proof of that. Now, how do we properly transfer these truths about the nation of Israel over to the individual gentile believer Paul speaks about? That's what we have to do properly.
To me, the olive tree metaphor is difficult to understand. Sometimes I think I get it, while at other times the concept slips away. So, maybe this time I should work backwards from Paul's conclusion and retrace his steps to see how he got there. Right? (smile) (I'm about to ramble on, putting my thoughts down for my own sake, not trying to convince you of anything. Feel free to follow along.)
What Paul is attempting to say is this. God made a promise concerning a future generation of Israel, that the entire nation would be considered holy and that he would bless them both materially and with eternal life. (Moses anticipates this future generation in Deuteronomy 29:22 and following.) Paul argues that a partial hardening has happened to Israel until the fulness* of the Gentiles has come in. But eventually "all Israel" shall be saved just as Moses predicted. Remember, Paul argues that God will spiritually bless and grant eternal life to all those whom he has chosen. Romans 11:7 In light of this, the question remains, who are the "chosen"? And didn't God chose Israel?
Paul argues that yes, in one sense, Israel itself is the chosen of God. But in another sense, the chosen of God are those individuals living in Israel whom God considers "holy". With regard to the Gentile nations, none of these other nations are God's chosen. However, for a time, God declared Gentiles to be "clean". Acts 10:15 In other words, God is now offering the Gentiles the same promise he made to the nation of Israel. And now, some among the Gentiles are considered "holy", because they are believers in Jesus Christ. But at some point in our future, the last remaining chosen Gentile will come to saving faith and confess Jesus as Lord. Thus ends the time of the Gentiles. Nonetheless, we conclude that even those among the Gentiles who came to saving faith were first "chosen" of God.
I can only conclude that the Olive Tree represents "the holy people whom God has chosen." God declared Israel to be his chosen people, but as Paul concluded, God wasn't referring to the Israel of today; he was referring to the Israel of tomorrow. THAT Israel is his holy people. The idea being expressed by branches being cut off the tree is roughly equivalent to the picture of a partial hardening. The promise concerns the nation of Israel, but over time, there has always remained those living in Israel who didn't love God, didn't fear God, and didn't obey God. These are not part of the "plaroma" the fullness. In the mean time, God has granted the Gentiles access to the promise and those among the Gentiles whom God has chosen, will be saved. But eventually, the Gentiles will grow arrogant and no longer love God, fear God and obey his gospel.
Anyway, if you have gotten this far, thanks for listening. As you can see, I need to do more work.
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*Note: Paul has coined the term "
plaroma:
fullness" to indicate the sum total of all believers throughout time. Thus, the "fulness" of the Gentiles would be the sum total of all Gentile believers who ever lived.