‘And Isaiah cries concerning Israel, “If the number of the children of Israel be as the sand of the sea, it is the remnant who will be saved, for the Lord will execute his word on the earth, finishing it and cutting it short.” '
He then cites from Isaiah 10:22 a (supplemented by Hosea 1:10) a verse concerning Israel which asserts that even though Israel should become very numerous, only a remnant of them would be saved, and this, as Isaiah 10:23 reveals, is as a result of the judgment of God on the remainder. This would support the case that the ‘all Israel' in Romans 11:26 who are saved means ‘the remnant'. ‘Finishing it' refers to the certainty of God's judgment', ‘cutting it short' might indicate that God stepped in to save the elect, or may indicate the speed with which the finishing will take place. In Isaiah 10 the prime reference of the verses is probably to deliverance from the Assyrians, although it may have included a wider reference to God's deliverance in terms of the more distant future (as prophecies often did). Paul seemingly sees it as including a principle which was permanently applicable, that in all God's dealings with Israel, only a remnant will be saved. So the teaching of Romans 9:26-28 is, in Paul's view, that only a remnant of Israel was to be saved, whilst numerous Gentiles were to become His people and His beloved, a situation which was true of the Christian church.
The LXX of these verses reads, ‘And though the people of Israel be as the sand of the sea, a remnant of them will be saved. He will finish the work, and cut it short in righteousness, because the Lord will make a short work in all the world.' (Isaiah 10:22-23 LXX). This has been supplemented at the beginning by ‘The number of the children of Israel be as the sand of the sea' which is found in Hosea 1:10. This combining of texts, with reference only being made to the major source, was commonplace in Paul's day. Compare a similar thing in Mark 1:2-3 where texts from Malachi and Isaiah are combined. We have no similar explanation for the rendering of Isaiah 10:23, although it is clear that while shortened, it does connect with the LXX text. This may have been found in the version from which Paul was citing, or it may simply have been his amendment of LXX. We simply do not know.