17 Some of the tree's branches were pruned and you wild olive shoots were grafted in. Yet the fact that you are now fed by that rich and holy root 18 gives you no cause to crow over the pruned branches. Remember, you aren't feeding the root; the root is feeding you. 19 It's certainly possible to say, "Other branches were pruned so that I could be grafted in!" 20 Well and good. But they were pruned because they were deadwood, no longer connected by belief and commitment to the root. The only reason you're on the tree is because your graft "took" when you believed, and because you're connected to that belief-nurturing root. So don't get cocky and strut your branch. Be humbly mindful of the root that keeps you lithe and green. 21 If God didn't think twice about taking pruning shears to the natural branches, why would he hesitate over you? He wouldn't give it a second thought.
Matthew Henry's Commentary on Romans 11:17-21
Commentary on Romans 11:11-21
(Read Romans 11:11-21)
The gospel is the greatest riches of every place where it is. As therefore the righteous rejection of the unbelieving Jews, was the occasion of so large a multitude of the Gentiles being reconciled to God, and at peace with him; the future receiving of the Jews into the church would be such a change, as would resemble a general resurrection of the dead in sin to a life of righteousness. Abraham was as the root of the church. The Jews continued branches of this tree till, as a nation, they rejected the Messiah; after that, their relation to Abraham and to God was, as it were, cut off. The Gentiles were grafted into this tree in their room; being admitted into the church of God. Multitudes were made heirs of Abraham's faith, holiness and blessedness. It is the natural state of every one of us, to be wild by nature. Conversion is as the grafting in of wild branches into the good olive. The wild olive was often ingrafted into the fruitful one when it began to decay, and this not only brought forth fruit, but caused the decaying olive to revive and flourish. The Gentiles, of free grace, had been grafted in to share advantages. They ought therefore to beware of self-confidence, and every kind of pride or ambition; lest, having only a dead faith, and an empty profession, they should turn from God, and forfeit their privileges. If we stand at all, it is by faith; we are guilty and helpless in ourselves, and are to be humble, watchful, afraid of self-deception, or of being overcome by temptation. Not only are we at first justified by faith, but kept to the end in that justified state by faith only; yet, by a faith which is not alone, but which worketh by love to God and man.