Psalms 64:6They search out iniquities; they accomplish a diligent search: both the inward thought of every one of them, and the heart, is deep.
Proverbs 18:4The words of a man's mouth are as deep waters, and the wellspring of wisdom as a flowing brook.
1 Corinthians 2:11For what man knoweth the things of a man, save the spirit of man which is in him? even so the things of God knoweth no man, but the Spirit of God.