Matthew Henry Commentary Romans 9:25-29

"As he saith also in Hosea, I will call that my people, which was not my people; And her beloved, that was not beloved. And it shall be, [that] in the place where it was said unto them, Ye are not my people, There shall they be called sons of the living God. And Isaiah crieth concerning Israel, If the number of the children of Israel be as the sand of the sea, it is the remnant that shall be saved: for the Lord will execute [his] word upon the earth, finishing it and cutting it short. And, as Isaiah hath said before, Except the Lord of Sabaoth had left us a seed, We had become as Sodom, and had been made like unto Gomorrah." — Romans 9:25-29 (ASV)

The rejection of the Jews and the inclusion of the Gentiles were foretold in the Old Testament. It greatly clarifies a truth to observe how Scripture is fulfilled in these matters. It is a wonder of Divine power and mercy that any are saved: for even those left as a seed, if God had dealt with them according to their sins, would have perished with the rest. This great truth is what this Scripture teaches us. Even among the vast number of professing Christians, it is feared that only a remnant will be saved.