en_tn_condensed/psa/064/006.md

The inner thoughts and hearts of man are deep

The writer speaks of man's "inner thoughts" and "hearts of man" as if they were a deep body of water that no one can explore all the way to the bottom. (See: rc://en/ta/man/translate/figs-metaphor)

inner thoughts ... hearts of man

Both of these phrases refer to man's private or inner thoughts. (See: rc://en/ta/man/translate/figs-doublet)