Romans 11:21

for if God spared not the natural branches, neither will he spare thee.

'This shows conclusively that Christians may conduct themselves in such way as to sever themselves from God's favor.' (Whiteside p. 235)

The argument is strong. 'As far as comparisons can be made at all in such things, the Jews had been more securely invested in the kingdom than the Gentiles. They were, in the language of the figure, not artificially grafted, but native branches....yet even that did not prevent Him from cutting off those who did not believe..' (Gr. Ex. N.T. p. 681)

'it would be. much less violent process to break off the wild olive branches (branches grafted in) than it was to break off those which belonged originally to the cultivated tree.' (Erdman p. 138)

It is amazing how people try to get around the teaching that this verse contains.

'Wuest says: "It should be clear that those in danger of being cut off are unsaved Gentiles, and not cut off from salvation, for they have none, but cut off from the place where God might use them, as unsaved Israel was cut off in the dispersion." Is that how the text looks to you?. (McGuiggan p. 330)