An excerpt from ch. 19 of my book on Romans, which analyzes much of Romans 11, where Paul explains how God works through the rejection of Israel to bring about salvation for all mankind:
“We should not try to take these practical explanations of God’s historical dealings with men and turn them into a basis for ideal theological principles beyond what they warrant. For example, what we have already mentioned, the stumbling of Israel was not literally necessary for the salvation of the Gentile. This is the practical view, though, of how God has brought it about. Likewise, we will see shortly that the salvation of the Gentiles has an important result also in God’s plan: The provoking of Israel to jealousy so that Israel too might turn and be saved. This is a practical view of what results from God’s dealings with men, but it is not to be thought that this was the only point and purpose of the salvation of the Gentiles or the necessary way by which alone the Jew could be saved. Could the Jewish nation only be saved by their initial rejection leading to the Gentile inclusion, which provokes them to jealousy to turn to Christ? No, but this is how God shapes and orders events in history to bring about His purposes. This is how it has and will actually take place.
This touches on the whole of God’s sovereignty in history. When we look at how God works to govern the affairs of all this world and the history of man, we are in a realm of great wonder and mystery. This is what Paul himself calls such dealings of God in this chapter, a “mystery” (11:25). We must learn to appreciate both the choices and actions of men as well as the greater and higher sovereignty of God over all men’s affairs in this world. There is no contradiction between the two, but God is wise and able to accomplish His purposes using men and their actions how He chooses.
While the rejection of the gospel by the Jews was the result of their own stubborn hearts against God’s will for them, not the result of God’s will for them, yet at the same time their rejection falls exactly into the larger picture of God’s plan to bring about salvation for all men. Regardless of what men might choose to do, God knows how perfectly to bring about the accomplishment of His will and purpose. All things are working together according to His ultimate will, which will most certainly be accomplished. This is the wonder of the mystery of God’s wisdom as seen in the whole workings of God’s plan in the world of men. And wondrous indeed it is, as Paul declares so loudly once he has laid out the whole picture in this chapter.“