Adam Clarke on 1 Corinthians 2:9

But, as it is written - The quotation is taken from Isa 64:4. The sense is continued here from verse seven, and λαλουμεν, we speak, is understood - We do not speak or preach the wisdom of this world; but that mysterious wisdom of God, of which the prophet said: Eye hath not seen, nor ear heard, neither have entered into the heart of man the things which God has prepared for them that love him. These words have been applied to the state of glory in a future world; but they certainly belong to the present state, and express merely the wondrous light, life, and liberty which the Gospel communicates to them that believe in the Lord Jesus Christ in that way which the Gospel itself requires. To this the prophet himself refers; and it is evident, from the following verse, that the apostle also refers to the same thing. Such a scheme of salvation, in which God's glory and man's felicity should be equally secured, had never been seen, never heard of, nor could any mind but that of God have conceived the idea of so vast a project; nor could any power but his own have brought it to effect.