en_tn/rom/11/18.md

do not boast over the branches

Here "the branches" is a metaphor that stands for the Jewish people. Alternate translation: "do not say you are better than the Jewish people God has rejected" (See: rc://en/ta/man/jit/figs-metaphor)

it is not you who supports the root, but the root that supports you

Again Paul implies that the Gentile believers are branches. God saves them only because of the covenant promises that he made to the Jews. (See: rc://en/ta/man/jit/figs-metaphor)