Jamieson, Fausset and Brown on 1 Corinthians 2:9

9. But--(it has happened) as it is written.

Eye hath not seen, &c.--Alford translates, "The things which eye saw not ... the things which God prepared ... to us God revealed through His Spirit." Thus, however, the "but" of 1Co 2:10 is ignored. Rather construe, as Estius, "('We speak,' supplied from 1Co 2:8), things which eye saw not (heretofore), ... things which God prepared ... But God revealed them to us," &c. The quotation is not a verbatim one, but an inspired exposition of the "wisdom" (1Co 2:6, from Is 64:4). The exceptive words, "O God, beside (that is, except) Thee," are not quoted directly, but are virtually expressed in the exposition of them (1Co 2:10), "None but thou, O God, seest these mysteries, and God hath revealed them to us by His Spirit."

entered--literally, "come up into the heart." A Hebraism (compare, Jr 3:16, Margin). In Is 64:4 it is "Prepared (literally, 'will do') for him that waiteth for Him"; here, "for them that love Him." For Isaiah spake to them who waited for Messiah's appearance as future; Paul, to them who love Him as having actually appeared (1Jo 4:19); compare 1Co 2:12, "the things that are freely given to us of God"