Hosea 1:10
Yet the number of the children of Israel shall be as the sand of the sea, which cannot be measured nor numbered; and it shall come to pass, that in the place where it was said unto them, Ye are not my people, there it shall be said unto them, Ye are the sons of the living God.
In the very place where the sentence of rejection had fallen, that they were not God's people, the opposite sentence would be spoken over them, that they are sons of the living God. At that same time the number of the children of Israel would become like the sand of the sea, beyond measure and beyond numbering. The promise joins the two reversals together, so that disowning is answered by sonship in that same place, and scattering is answered by an innumerable multitude.
The verse foretells the gathering of the Gentiles into God's church and people, with the result that those once disowned are recognized as God's people and sons and Israel itself is enlarged. Its pledge of a multitude that cannot be counted is fulfilled in the gospel's ingathering of the Gentiles, when whole Gentile communities receive the gospel. Those believing Gentiles become a new Israel grafted into the old olive tree. Jewish unbelief, opposition, and rejection do not block this merciful purpose, for God did not cast away Israel even though Israel rejected His Son, but purposed that His grace should be revealed among Gentiles as well as among Israelites, calling His people not from the Jews only but also from the Gentiles.
Among the Israelites scattered in judgment and exile, those who remained faithful to God or humbled themselves before Him seeking pardon and peace are counted as the sons of the living God. Through those faithful captives God would bring many people in the Assyrian realm to know His character and the goodness of His law.