9:27 {26} Esaias also crieth concerning Israel, Though the number of the children of Israel be as the sand of the sea, a remnant shall be saved:
(26) Contrary to this, neither any outward general calling, neither any worthiness of our ancestors, is a sufficient witness of election, unless by faith and belief we answer God's calling: which thing came to pass in the Jews, as the Lord had foretold.
9:27 Esaias also crieth. See Isa 10:22. Not only do the prophets show that the Gentiles are to be called, but that a great part of Israel is to fall from God. The passage says that though the people of Israel become numerous as the sands of the seashore, only a remnant shall be saved. This prophecy originally applies to the return of the Jews from the Captivity, but, like many other prophecies, has a double application.
9:27 But Isaiah testifies, that (as many gentiles will be accepted, so) many Jews will be rejected; that out of all the thousands of Israel, a remnant only shall be saved. This was spoken originally of the few that were saved from the ravage of Sennacherib's army. Isa 10:22,23
9:25-29 The rejecting of the Jews, and the taking in the Gentiles, were foretold in the Old Testament. It tends very much to the clearing of a truth, to observe how the Scripture is fulfilled in it. It is a wonder of Divine power and mercy that there are any saved: for even those left to be a seed, if God had dealt with them according to their sins, had perished with the rest. This great truth this Scripture teaches us. Even among the vast number of professing Christians it is to be feared that only a remnant will be saved.