18 do not boast against the branches. But if you do boast, remember that you do not support the root, but the root supports you.
18 do not boast against [exult over] the branches.
There was no reason for Gentiles to brag about being grafted into the cultivated olive tree because it was a matter of faith, not works.
The word “boast” means to exult over. It was used for a gladiator exulting over his conquered foe. The idea Paul presented here was, “Gentiles, do not forget where you came from.” Gentiles owed Jews something.
But if you [Gentiles] do boast,
Paul gave the reason why it was not proper for Gentiles to boast about being grafted into the tree.
remember that you [Gentiles] do not support the root [God’s covenant with Israel],
Gentiles did not support the root of the tree, but the root supported them. The root of the tree supports the life of the tree. Gentiles were linked to the Abrahamic Covenant by third-party blessing.
but the root [Israel] supports you [Gentiles].
There was a temptation for Gentiles to believe that they were more special in God’s eyes because the effort to graft them into the tree as wild branches. Gentiles owed their spiritual heritage to Israel, not themselves. Salvation of both Jew and Gentile came through the blessings of the Abrahamic Covenant.
This section of Romans does not say that Gentile believers became part of Israel but only that they participated in the blessings of Israel. The olive tree is not the church but the wild branches benefit from the root of the tree. It is God’s faithfulness to His covenant with Abraham to bless the nations that is at issue. Believing Gentiles are now in the place of Israel’s blessing.
God grafts people into eternal life by His grace.
Grace is not exclusive for either Jew or Gentile. Neither group can lord it over the other by a claim that they have a special grace from God that the other does not. Gentiles need to remember that their heritage of grace came from God’s blessing on Israel.