Surah 20. Ta-Ha, Ayah 7

I.e., He knows not only man’s unspoken, conscious thoughts but also all that goes on within his subconscious self.

There are two or three implications. (1) Whatever you profess, or say aloud, gives no information to Allah: He knows not only what is secret and perhaps unknown to others, but what people take special care to conceal. (2) It does you no good to make insincere professions: your hidden motives are known to Him, Who alone matters. (3) If you read the Word of Allah, or if you pray to Allah, it is not necessary to raise your voice: in either case, Allah will judge you by your inner thoughts which are like an open book to Him.