A.T. Robertson Commentary Romans 9:25

"As he saith also in Hosea, I will call that my people, which was not my people; And her beloved, that was not beloved." — Romans 9:25 (ASV)

In Hosea (εν τω Hωσηε). He quotes 2:23 with some freedom. Hosea refers to the ten tribes and Paul applies the principle stated there to the Gentiles. Hosea had a son named Lo-ammi = ου λαος. So here ο ου λαος μου "the not people of mine." Ου with substantives obliterates the meaning of the substantive, an idiom seen in Thucydides and other Greek writers. See also Ro 10:19; 1 Peter 2:10.

Which was not beloved (την ουκ ηγαπημενην). The LXX rendering of Lo-ruhamah (not mercy, without mercy or love), name of Hosea's daughter. The use of ουκ with the perfect passive participle is emphatic, since μη is the usual negative of the participle in the Koine.