John Calvin on Hosea 1:9

The reason is added For ye are not my people, and I will not hereafter be yours. This, as I have said, is the final disowning of them. They had been before called Jezreelites, and then by the name of the daughter God testified that he was alienated from them; but now the third name is still more grievous, Ye are not my people; for God here abolishes, in a manner, the covenant he made with the holy fathers, so that the people would cease to have any preeminence over other nations. So then the Israelites were reduced to a condition in which they differed nothing from the profane Gentiles; and thus God wholly disinherited them. The Prophet, doubtless, was not well received, when he denied them to be God’s people, who had yet descended from Abraham according to the flesh, who had ever been so accounted, and who continued proudly to boast of their election.

But let us hence learn, that those awfully mistake who are blind to their own vices, because God spares and indulges them. For we must ever remember what I have said before, that the kingdom of Israel was then opulent; and yet the Prophet denies them, who flourished in strength, and power, and riches, to be God’s people. There is then no reason for hypocrites to felicitate themselves in prosperity; but they ought, on the contrary, to have regard to God’s judgement. But though these, as we see to be the case, heedlessly despise God, yet this passage reminds us carefully to beware lest we abuse the present favours of God. It follows —

Hosea 1:10

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.

10. Et erit numerus filiorum Israel tanquam arena maris, quae non mensuratur et non numeratur, (non mensurabitur nec numeratur, ad verbum sed significant haec verba actum continuum, et est indefinita etiam locutio;) et erit in loco ubi dicetur, (hoc est, ubi dictum fuerit eis,) Non populus meus vos; et dicetur (hoc est, illic dicetur) Filii Dei vivi.