Here "heart" is a metonym for a person's thoughts. This can be stated in active form. Alternate translation: "God would reveal to him the secrets of his heart" or "He would recognize his own private inner thoughts" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-activepassive]])
"Fall on his face" here is an idiom, meaning to bow down. Alternate translation: "He would bow down and worship God" (See: [[rc://en/ta/man/translate/figs-idiom]])