1 Corinthians 2:9 - Ellicott's Commentary On The Whole Bible

As it is written. — Where do the words which follow occur? They are not to be found as here given anywhere in the Old Testament. It has therefore been suggested (Origen) that they are from some apocryphal book, or some book which has been lost, as is supposed many have been. Chrysostom also suggests that it may be a reference, not to a writing, but to historical facts, as in Matthew 2:23. None of these explanations would justify the use of that phrase, “it is written,” with which these words are introduced, and which in the apostolic writings is confined to quotations from the Old Testament scriptures. It is not used where the words are taken from other sources (see, e.g., Jude 1:9; Jude 1:14). Although the words given here are not to be found in the same sequence in any passage in the Old Testament, still there are phrases scattered through the writings of Isaiah (see Isaiah 64:4; Isaiah 65:17; see also Isa 62:15 in the LXX.), which would easily be joined together in memory and resemble even verbally the passage as written here by the Apostle. This is not the only place in which St. Paul would seem to thus refer to the Old Testament scriptures (see 1 Corinthians 1:19-20) when he is not basing any argument upon a particular sentence in the Scriptures, but merely availing himself of some thoughts or words in the Old Testament as an illustration of some truth which he is enforcing.