Romans 11:18

‘Do not glory over the branches. But if you do glory, it is not you who bears the root, but the root you.'

The assumption here might be that Gentile Christians in Rome have been gloating over the situation as regards unbelieving Israel. It may, however, simply be that Paul foresees the danger of that happening (having seen it elsewhere) and is simply trying to prevent it. But that there were differences between Jewish and Gentile Christians in Rome comes out in Chapter s 14-15. Whichever way it is, his point is that they should not so glory in themselves, but should rather remember what they owe to Israel as the producer of the Messiah (Romans 9:5), and the preserver of God's oracles (Romans 3:2). They owe what they now are to the root. Let them rejoice in what their salvation has brought. But let them not despise those who already had the word of God, even though they did hold it in unbelief. For their blessing has come from the root of Israel in one way or another. It is significant that the branches are seen as being borne by the root rather than the tree, for this closely connects the root with the tree and therefore connects with Romans 11:16, ‘and if the root be holy so are the branches'.