Allah SWT sent down the revelation that is the literal speech of Allah and it was sent by a noble honoured trustworthy messenger who obeys to another noble trustworthy honoured messenger who obeyed the commands of Allah. The angelic Jibreel conveyed the message of the Quran sent from Allah to the noble messenger Muhammad peace be upon him. Allah SWT directly confirms and attributes those noble qualities to Jibreel and Muhammad peace be upon him and states that these words are not the prose of a poet as the disbelievers claimed because they had no faith nor is the words of a fortune teller or soothsayer as the disbelievers are not mindful of the Quran and its message. The Quran is a revelation to all the worlds from Allah sent to Muhammad peace be upon him and informs the people that the Prophet Muhammad peace be upon him never added, omitted or made up anything or spoke from himself with regard to the Quran and conveyed the message in its original form just as it is still preserved and guarded to this day.
Allah SWT states that had the Prophet Muhammad peace be upon him tried to change or make up any aspect of the Quran from himself then he peace be upon him would have been seized and no one could have prevented Allah from severing his aorta the blood vessel to the heart and then he peace be upon him would have been subject to a severe punishment. Allah SWT says no one could have shielded or protected this from happening by Allah had he peace be upon him tried to change or make up the words of the Quran from his own desires.
And finally Allah SWT mentions how the Quran is a reminder to those people who are God conscious of Allah and within their hearths the aspects of taqwa which is enjoining what is good and prescribed from Allah and staying away from what is evil and prohibited by Allah. Only those people who are fearful of Allah and have taqwa benefit from the reminder of the Quran as the words of the Quran are a guide and healing for the hearths of those mindful of Allah otherwise those who are in denial will be in anguish and misguidance due to the Quran just as disbelievers will be on the day of judgement. The Quran is a means by which people will heavy and anguish for not believing in its message causing them to be misguided due to their denial and persistence in disbelief resulting in the inevitable anguish and suffering on the day of reckoning.
Whereas the Quran for those who are fearful and conscious of Allah will find it a means of light and also salvation from the severe trials and tribulations of the earth and the day of judgement. The Quran will be witness to the people as to whether they recited, understood and lived by it and the Quran is a means of joy and comfort to the hearts of the believers.