If you truly want to benefit from the Qurʾān, your heart must be attentive and alert when reciting it or listening to it. Listen to it carefully with presence of mind, paying attention to it as if Allāh Himself was speaking to you directly. Understand that this Qur’ān is addressed to you from Allāh, Most High, upon the tongue of His Messenger ﷺ.
“Truly there is a reminder in this for anyone who has a heart, or who listens attentively with presence of mind.”
A deep and lasting impression is dependent upon the presence of something that will stimulate a person, a focal point, the right frame of mind, and the absence of anything that would impede the impression from taking effect. This verse mentions of all of these in the most succinct and lucid of ways:
“Truly there is a reminder in this” refers to the previous verses of this chapter. This, the Qurʾān, is the stimulus.
“for anyone who has a heart” refers to the focal point which is to be stimulated. The heart referred to here is the living heart: the heart that is aware of Allāh. He, Most High, says,
“it is simply a reminder and a clear Qur’ān so that you may warn those who are truly alive,”
i.e. those whose hearts are alive.
“or who listens attentively,” i.e. directs his faculty of hearing towards it and pays it the utmost attention. This is the condition that must exist for a person to be roused by the words.
“with presence of mind,” i.e. with an alert and present heart, not one that is unmindful and absent. Ibn Qutaybah said, ‘i.e. a person who listens attentively to Allāh’s Book with presence of heart and mind, not someone who is unmindful with an absent air.’ This then alludes to the barrier: an unmindful and inattentive heart that does not understand what is said and, as such, is unable to reflect upon it or direct any conscious thought towards it.
Therefore, if all these things come together, the end-result is achieved: benefiting from the Qurʾān and taking heed.
If someone were to ask: if the end-result, the lasting impression, is only attained by the combination of these matters, why then did Allāh say “or” in the verse, “or who listens attentively” which implies a choice between one or another option? Surely “and” should have been mentioned in its place?
This is a good question; the answer is that “or” has been mentioned because what is being considered is the state of the addressee.
Some people have hearts which are full of life, hearts that will readily accept the truth and whose innate nature (fiṭrah) is intact; if such a person was to reflect just in his heart and turn his mind to it, he would conclude that the Qurʾān is authentic and true. His heart would bear witness to the truth of the Qurʾān and the subsequent impression of its verses would be as light layered on top of the light of its innate nature. This is the description of
those about whom it is said,
“those who have been given knowledge see that what has been sent down to you from your Lord is the truth.”
Concerning them, Allāh says,
“Allāh is the Light of the heavens and the earth. The metaphor of His light is that of a niche in which there is a lamp, the lamp inside a glass, the glass like a brilliant star, lit from a blessed tree, an olive, neither of the east nor the west, its oil all but giving off light even if no fire touches it. Light upon light! Allāh guides to His Light whoever He wills, Allāh propounds metaphors for mankind and Allāh has knowledge of all things.”
This verse refers to the light of the innate nature covered by the light of revelation; this is the condition of the person who has a living, receiving heart. We have explained this verse, its subtleties and lessons in detail in our book, Ijtimā’al-Juyūshal-Islāmiyyah ‘alā Ghazw al-Muɼaṭṭila wa’l-Jahmiyyah.
Therefore, the person who has this type of attentive heart receives the meanings of the Qurʾān and readily accepts them so much so that it seems as if the words are inscribed in his heart and he is able to recite them fluidly from memory.
Other people have hearts that fall below the level of those mentioned above; their hearts are not as ready to receive the truth, they are not completely alive, and their innate nature is not as refined. Therefore, they stand in need of a witness who would differentiate the truth from falsehood for them. In order to be guided, such a person must pay the utmost attention to the Qurʾān’s words, he must devote his heart to it, ponder it and comprehend its meanings, and only after this will he come to realise that it is true.
The first type of person sees the truth of what he is invited to and informed of with his own eyes. The second type of person has learned that it is the truth, has certainty in it and is satisfied. The first has attained the ranking of beneficence, iḥsān and the second has attained the ranking of faith, īmān. The first has attained ‘ilm al-yaqīn from which his heart ascends to the degree of ‘ayn al-yaqīn. The second has acquired that level of unwavering belief that takes him out of the fold of disbelief and into the fold of Islām. 
‘Ayn al-Yaqīn is of two categories: what is acquired in this world and what is acquired in the Hereafter. In this world it is to the heart what the beheld is to the eye. All the matters of the unseen that the Messengers informed us of will be seen by the eye in the Hereafter and the inner sight in this world; in both cases, this is ‘ayn al-yaqīn.
-  Ibn Qutaybah, Gharību’l-Qur’ān, pg. 419
-  Ibn al-Qayyim, Ijtimā’, pp. 6-12. He also discussed this verse in al-Wābil al-Ṣayyib, pp. 65-68, I’lām al-Muwaqqi’īn, vol. 1, pp. 205-209, al-Ṣawā’iq al-Mursalah, vol. 3, pg. 851
-  i.e. he has acquired the station of ‘ilm al-yaqīn