1 Corinthians 2:9

that the natural man cannot understand it.
Overview - 1 Corinthians 2
He declares that his preaching, though it bring not excellency of speech, or of human wisdom, yet consists in the power of God;
and so far excels the wisdom of this world, and human sense,
Treasury of Scripture Knowledge

1 Corinthians 2:9  (King James Version)
But as it is written, Eye hath not seen, nor ear heard, neither have entered into the heart of man, the things which God hath prepared for them that love him.

This passage is not taken from the LXX., nor is an exact translation of the Hebrew; but it gives the general sense.
Isaiah 64:4 ; John 3:16 ; 1 Peter 1:12

the things
Psalms 31:19 ; Matthew 20:23 ; 25:34 Hebrews 11:16

Romans 8:28 ; James 1:12 ; 2:5 1 John 4:19