Adam Clarke on 1 Peter 2:10

Which in time past were not a people - This is a quotation from Hos 1:9, Hos 1:10; Hos 2:23, where the calling of the Gentiles, by the preaching of the Gospel, is foretold. From this it is evident, that the people to whom the apostle now addresses himself had been Gentiles, covered with ignorance and superstition, and now had obtained mercy by the preaching of the Gospel of Christ.