So those who don't believe are cut off from "true Israel," which means they are separated from Christ (the root) and the Spirit (the nourishment)?
But doesn't being cut off from something imply one was once attached to it? How is one attached to Christ and being nourished by the Spirit get detached?
This is where you take the allegory too far. It's kind of like taking the Parable of the Unjust Judge too far and concluding that God only answers our prayers to get us off His back. The point of the parable was to pray and not grow weary of it, even though from our point of view God has turned a deaf ear to us.
The point of Paul's allegory is that the Israel of God is made up of people from all families of the earth, that they who stand, stand by faith, and that God is no respecter of persons.
You say you're a jew? So what? God can make jews of these rocks laying here.
These Jews who were cut off, were they once attached to the true Israel, Christ (the root) and the Spirits nourishment?
From our point of view, the corrupt natural branches appeared to have been a part of the Israel of God all along, and are simply being cut off now because of the Gospel. The temptation of people from other families is to think the jews were cut off to make room for them, but Paul is plain, they were cut off because of unbelief. It isn't that they believed and then quit believing. They had always abided in unbelief, though they reaped the carnal benefits of the blessings of God under the Old Testament, e.g., prosperity, safety, nobility, etc. But now the judgment of God has come upon their unbelief. It's now apparent that the law and the prophets have been fulfilled, and though they once knew Christ by the flesh, they now know Him that way no more, 2 Cor. 5:16. There is no more temple, no more sacrifice, no more priesthood. No one may approach that way anymore.
Those in unbelief never were a part of the Israel of God. But the tree is being purged and the wild olive branches,
sheep not of this fold, are being grafted in. So
all Israel will be saved.
Couldn't it just be that the tree represents the revelation of God by which men respond either in faith or unbelief? Special revelation came through Israel thus making them the natural branches, but now the revelation is coming through the church which the Gentiles are joining in great numbers...being grafted into the revelation of God so as to respond either in his "kindness" or in unbelief and pride.
No, and even naturally speaking that's a reach. If that were the case it would seem the people would be better represented not as branches, but as gleaners picking the fruit.
What do you mean by "stand?"
Stand. IOW pleasing to God. Living justly.
Are you equating that with being grafted in the tree?
Abiding in the tree, yes. It's the root, Christ, that bears us, and the Spirit that gives us life.
And falling with being "cut off" of the tree? Explain
No. Being cut off is a judgment.