Again Your foundation is different than mine. Thats why we will never agree,
Again, It is not talking about salvation. You are placed into the vine to produce fruit, not be saved. The context is Israel vs Gentile. Who has control of Gods word. Who is given the responsibility of being God representation.
Isreal had a few thousand years, They failed over and over. So God took it from them, and gave it to the gentiles. Pauls warning is for us to not be ignorant of the mystery, and we have some how made it.
Either way, Again it does not matter. John said a person who left never was saved. So you can not use it anyway without causing a major contradiction in the word of God.
The word of God is not Romans 11. It is the whole book.
Paul isn't talking about producing fruit in this application, he talking being in or belonging to the family of God by using the picture of a cultivated olive tree.
This may come to news to you, but Israel was never selected or chosen for salvation. They, Abraham, was chosen to be a missionary to the world. The Abrahamic covenant was a promise to Abraham that his seed (singular, meaning Christ) will bring blessings to all families of every nation (this was unconditional). The promise was that all nations will be blessed through him. And the sign of this covenant was circumcision, not natural descent. Anyone, gentiles, could be included and were included, as long as they were circumcised. If a natural Jew wasn't circumcised, they were to be cast out of the covenant. The Jews were never selected or chosen specifically for salvation, even though many were saved as a consequence of God choosing Abraham for God's plan of redemption.
2nd, John gives one example of someone leaving the church because they weren't "part or of them", John is not saying this applies to everyone who leaves the church or loses their faith. John is not building a church doctrine here.
God took the Kingdom from the religious leaders of Israel and gave not to just gentiles, but first to the Jews, who do you think 12 disciples were? They were Israelites! The remnant! Luke 12:32, Jesus speaking to Jewish disciples of Christ,
"Do not be afraid, little flock, for your Father has chosen gladly to give you the kingdom."