Clearly the branches represent here are in reference to Israel and the Gentiles. Israel is being "cut/broken off" but can be "grafted back in" "if they do not persist in unbelief." The Gentiles are being "grafted in" but can be broken off if they do not continue in faith. Now, if you take this as "individuals" who are being grafted in and cut off from salvation, then you would have to violate the doctrine of Perseverance. But, if Paul is referring to Nations (corporately) then the question is what does the vine represent? Some say the church or the gospel. So, you have the Gentiles being grafted into His church, granting them the ability to enter covenant through faith in His gospel appeal. That gospel appeal is being hidden (spirit of stupor/parabolic language) from Israel temporarily so as to allow room for the Gentiles. What say you?