Paul has just described a hardening in Israel, and he refuses to let anyone conclude that the story is over. 11"did they stumble in order that they might fall?" The answer is no. Even the stumbling has a purpose folded into it. Salvation has come to the Gentiles through Israel's trespass, and it is meant to make Israel jealous. What looks like a dead end is a road with a turn in it.
Then Paul speaks directly to his Gentile readers, and the tree arrives to carry his point. 17"you, although a wild olive shoot, were grafted in among the others," and so 18"do not be arrogant toward the branches." A wild shoot grafted into cultivated stock draws its life from a root it did not plant and cannot take credit for. 18"it is not you who support the root, but the root that supports you." Every Gentile believer reading the letter owed the whole of their spiritual life to a tree planted long before they arrived.
Paul hears the boast forming already. The Gentile says, "Branches were broken off so that I might be grafted in." Paul grants the point and turns it into a reason for humility. 20"you stand fast through faith. So do not become proud, but fear." Belonging to the tree was always a matter of faith, for the branches cut off and the branches grafted in alike. Faith held them there, and unbelief could cut anyone off, wild shoot or natural branch.
Then comes a sentence that refuses to let either half cancel the other. 22"Note then the kindness and the severity of God." Severity toward those who fell is sobering. Kindness toward those grafted in is sustaining, provided you continue in it. Neither kind of branch stays attached by its own strength. Both stay attached by remaining where grace placed them.
Finally the argument reaches its point. 23"God has the power to graft them in again." What happened to the Gentiles was the stranger miracle. Ordinary grafting takes a cultivated branch and improves wild stock. Paul says God did the reverse, a wild shoot set into a cultivated tree, contrary to nature (verse 24). If God has already done the unnatural graft once, putting the natural branches back into their own tree, the tree they grew from, is the easier work.
The passage asks two things of anyone who reads it as a Gentile believer. Give up any pride of position, because you stand by faith in a root you did not plant. And refuse to write off the people who once belonged to that root. The God who grafted you in against every rule can do it again for them, and he asks you to pray and live with that hope in view. Paul asks this as someone who loves both branches: he calls himself an apostle to the Gentiles and says he magnifies that ministry in the hope of making his own people jealous and saving some of them (verses 13-14).
Prayer
Father, thank you that the root we draw our life from is one we never planted. Keep us from the arrogance of forgetting that we stand by faith and by your kindness, grafted in against every rule grafting follows. We ask boldly for what this passage points toward: graft the natural branches back into their own tree, as you have the power to do. In Jesus' name, amen.