Paul says basically the same thing twice for emphasis. AT: "he would realize that he is guilty of sin because he hears what you are saying" (See: rc://en/ta/man/translate/figs-parallelism)
"The secrets of his heart" here is a synecdoche for "private inner thoughts." This can be stated in active form. AT: "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-activepassive and rc://en/ta/man/translate/figs-explicit and rc://en/ta/man/translate/figs-synecdoche).
"Fall on his face" here is an idiom, meaning to bow down. AT: "He would bow down and worship God" (See: rc://en/ta/man/translate/figs-idiom)