Romans 11:13-27
13 For I speak to you Gentiles, inasmuch as I am the apostle of the Gentiles, I magnify mine office:
14 If by any means I may provoke to emulation them which are my flesh, and might save some of them.
15 For if the casting away of them be the reconciling of the world, what shall the receiving of them be, but life from the dead?
16 For if the firstfruit be holy, the lump is also holy: and if the root be holy, so are the branches.
17 And if some of the branches be broken off, and thou, being a wild olive tree, wert graffed in among them, and with them partakest of the root and fatness of the olive tree;
18 Boast not against the branches. But if thou boast, thou bearest not the root, but the root thee.
19 Thou wilt say then, The branches were broken off, that I might be graffed in.
20 Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear:
21 For if God spared not the natural branches, take heed lest he also spare not thee.
22 Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off.
23 And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again.
24 For if thou wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be graffed into their own olive tree?
25 For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in.
26 And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob:
27 For this is my covenant unto them, when I shall take away their sins.
The Grace New Testament Commentary - Romans 11:15-23
11:15-16 God has definitively not repudiated Israel, but He has cast them to one side, which has led to the reconciling of the world. Reconciliation refers to the same truth he has already referred to in Romans 5:10-11. The believer has "peace with God" (Romans 5:1). But for Paul that reconciling work was accomplished for all mankind, thus making possible the reconciliation of each person when he turns to Jesus Christ in faith (cf. 2 Cor 5:19-20). But if such a superlative benefit accrues to the world through throwing Israel aside, how could one describe the potential benefit of Israel being received back into God's gracious favor? The restoration of Israel would be like life from the dead.
In the end times, when Israel is back in its favored position, the entire world will experience a transformation for the better. The believing remnant should be construed as a kind of first fruits which prefigure the future transformation of the entire batch of dough, that is, of the entire nation. Israel's root is holy with the result that the branches that have sprung from it are likewise holy. By the term root it is natural to understand a reference to Abraham who is physically the source of the entire nation. So despite the catastrophic fall of the nation, the branches sprung from the Abrahamic root remain holy to God.
11:17-18 The view that Israel's present status was permanent could easily lead to what amounted to prideful Gentile exultation that in this new situation the Gentiles themselves were God's favored people. Paul's warning is that they should by no means exult over the branches. They were merely branches taken from a wild olive tree and grafted in among the original branches after many of those branches were broken off.
It is natural to think of Paul's reference here to the root as a reference to Abraham from whom the entire nation had sprung. The uncultivated olive tree is accordingly the Gentile world. If the Gentiles had been grafted in, it was not at all the case that they brought inherent value to the olive tree to which they were now spiritually connected. They had simply become a sharer in the spiritual advantages that flowed from the root into the tree. Humility was thus in order for Gentile believers. The Gentiles who believe have received the blessing of Abraham (justification by faith; Gal 3:6-14). Yet the richness Paul mentions goes well beyond this fundamental blessing. It suggests all the ensuing benefits that come from being placed in close connection to God's ongoing purposes with His ancient people.
11:19-21 Paul admits that the Jews were broken off so that the Gentiles could be grafted in. But it is not a legitimate ground for pride since the issue is not "merit" (i.e., works), but rather an issue of unbelief and faith. What the natural branches lost in their unbelief, the Gentiles gained by faith. But it was not simply that they gained it by faith, but instead that they now stand by faith. They can only retain their position on the olive tree if they maintain their faith.
This, of course, has nothing to do with the issue of individual perseverance in the faith, or with anyone's individual eternal destiny. This is a collective personification of the Gentiles that intends to describe their present privileges as the product of their believing response to the gospel. Accordingly, he cautions, Don't be haughty, but be afraid. Very simply put, should the Gentile world cease to be a responsive instrument for the gospel, God could return His focus to Israel.
11:22-23 God's kindness was the source of the Gentiles present privilege, while those whom God originally favored with His kindness (i.e., the Jews) had now tasted His severity. The loss of the former (kindness) resulting in the latter (severity) could easily be repeated for the Gentiles. God's kindness should not be taken for granted.
The kindness that the Gentiles currently enjoy is conditional: "if you remain in that kindness". If the Gentiles do not continue to be responsive to the truth of the gospel, they can be removed from the olive tree: "Otherwise you too will be cut off". This means that the Gentiles collectively will forfeit their privileged place in the ongoing purposes of God and will cease to be the primary instrument for the spread of the gospel.
But if the Gentiles are cut off, the restoration of Jewish privilege can also take place, provided that they (the Jews) do not remain in unbelief. The issue hinges on whether the Jews continue their massive rejection of the gospel message. However, if they do not, the Jewish nation shall be grafted in, precisely because God is fully able to put them back where they were in the first place.