Remember: you do not bear the root, but the root bears you!

Isa 11:1  But a branch (a Netzar) will emerge from the trunk of Yishai (Jesse), a shoot will grow from his roots.

Rom 11:17  And if some of the branches were broken off, and you, being a wild olive tree, have been grafted in among them, and came to share the root and fatness of the olive tree,
Rom 11:18  do not boast against the branches. And if you boast, remember: you do not bear the root, but the root bears you!

If some of the branches, that is, unbelieving individual Jews but not the whole Jewish people, were broken off, removed (temporarily, not permanently! Rom_11:11-12, Rom_11:23-24) from being eligible to receive what Yehovah God has promised, and you Gentiles (Rom_11:13), a wild olive, were grafted in among them, among the branches which are still part of the tree, the Messianic Jews, the Jewish nation as represented by its Messianic Jewish community, and have become equal sharers in the rich root of Yehovah God's cultivated olive tree, then don't boast as if you were better than (literally, "don't boast against") the natural branches, neither the ones still in place (the Messianic Jews) nor the ones broken off (the non-Messianic Jews). Gentile pride in having been joined to the "chosen people" is utterly out of place, particularly when directed against those very people! As Sha'ul writes elsewhere, "After all, what makes you so special? What do you have that you didn't receive as a gift? And if in fact it was a gift, why do you boast as if it weren't?" (1Co_4:7)

However, if you do boast, for whatever reason-carelessness, thickheadedness, or actual malice-it ought to help you stop if you remember that you are not supporting the root, but the root is supporting you. Or, to make Sha'ul's point as clear as it can be, whether the root is Yeshua, Avraham, the Patriarchs, the Messianic Jews or all the Jews (see Rom_11:16), it is a Jewish root, and don't you forget it! The Jewish community sometimes draws a picture of the Jew who comes to faith in Yeshua as someone doubly unwelcome, rejected both by other Jews and by the Gentile majority in the Church as well. It's easy enough to understand why a Messianic Jew might be rejected by some in the Jewish community, but why did the image of his being rejected by the Church even arise? It came from Gentile Christians who forgot Sha'ul's warning and regarded the Jewish believer in their midst not as a natural branch of the olive tree into which they were grafted, but as an alien.

Shifting the perspective slightly, notice that Sha'ul is reminding Gentile kedoshim (set-apart ones) and in this modern day (Christians) that trusting Yehovah God also means joining  God's people. It is no different now than it was with Ruth: "Your people shall be my people and your Elohim my Elohim" (Ruth_1:16).

Kedoshim (set-apart ones) and in this modern day (Christians) have joined Yisrael, not the reverse (see also Eph_2:11-16). For a kedoshim (set-apart ones) and in this modern day (Christians) to look down on the people he has joined is not only chutzpah and ingratitude but also self-hate.