The language comes from Hosea 2:23. Hosea had been instructed to name his son “Not My People” as a living warning to Israel that their apostasy had prompted God to disown them (Hosea 1:9). Yet God promised to have mercy and work repentance among his people (Hosea 2:14–15). As a result, he would again say to Israel, “you are my people” (Hosea 2:23). Peter’s readers had historically not been God’s people (for they were Gentiles, 1 Peter 4:2), but the Lord God had worked in their hearts the same repentance he had promised in Hosea 2:14–15 (= rebirth). So the claim that resulted in Hosea 2:23 belongs to the exiles of the Dispersion too: they are God’s people. The phrase also links back to 1 Peter 2:9 where the apostle had described his readers as “a people for his own possession.” This identity gives further shape to the “excellencies” these elect exiles may “proclaim.”
10 Once you were not a people, but now you are God’s people; once you had not received mercy, but now you have received mercy.