'On your heart' means: O Muhammad, who is the noblest of hearts and the highest of them, and the most precise and aware of them. There is no deviation in it nor crookedness. Until it became a character for him. In the omission of the intermediary, there is an indication that due to the intensity of his reception of the hearing and his presence of the senses, he becomes so capable of it that he preserves it and does not forget it. He understands it with true understanding so that it does not escape him. Thus, its entry into the heart is in the utmost ease, as if it reached him without the intermediary of hearing, unlike what comes from the criminals. And likewise, everyone who comprehends something with utmost comprehension preserves it completely. Look at His saying, 'And do not hasten with the Qur'an before its revelation is completed to you, and say, 'My Lord, increase me in knowledge' [Ta-Ha: 114] 'Do not move your tongue with it to hasten it' [Al-Qiyama: 16]. And since the context in this surah is for warning, he said, justifying the previous sentence: 'So that you may be among the warners,' meaning: the ones who frighten and warn those who turn away from faith and commit what they have been forbidden from disobedience.