Polishing the Hearts
The believer is in dire need of remembering Allāh and this remembrance is what preserves the heart.
Whoever neglects [remembering Allāh] most of the time, then his heart will become rusty in accordance with how neglectful he is.
Allāh - the Most High - said:
“O you who believe! Remember Allāh and remember Him a lot.” [Sūrah al-Aḥzāb 33:41]
“Those men and women who remember Allāh a lot.” [Sūrah al-Aḥzāb 33:35]
“So when you have finished the rights of your Pilgrimage, then remember Allāh as you remember your forefather, or with more intense remembrance.” [Sūrah al-Baqarah 2:200]
These verses contain a command to remember Allāh intensely and abundantly, since the worshipper is in dire need of (remembering Allāh) and cannot do without it even for a twinkling of an eye. This is because every muʿmīnt that a person does not spend in the dhikr (remembrance) of Allāh will not be of any benefit to him. Rather, the harm entailed in being neglectful of the dhikr of Allāh is far greater than any benefits that can be gained. One of the ’aarifīn (those who are knowledgeable about Allāh) said: “If a person were to spend such and such number of years engaged (in the dhikr of Allāh), then he turns away from it for just a muʿmīnt, what he will lose is far greater than whatever he has already gained.” So al-Bayḥaqī relates from ’Aa‘ishah (raḍī Allāhu ’anhaa) that the Prophet (ṣallallāhu ʿalayhi wa-sallam) said: “There is no time in which the son of Ādam does not remember Allāh in it, except that it will be a source of regret for him on the Day of Judgement.”  Muʿādh Ibn Jabal (raḍī Allāhu ʿʿʿanhu) relates that the Prophet (ṣallallāhu ʿalayhi wa-sallam) said: “The people of Paradise will not have any regrets except for those muʿmīnts in which they were not engaged in the dhikr (remembrance) of Allāh.”  Muʿādh Ibn Jabal also relates that Allāh’s Messenger (ṣallallāhu ʿalayhi wa-sallam) was asked: What action is the most beloved to Allāh? So he replied: “That you continue to keep your tongue moist with the dhikr of Allāh, until you die.” 
POLISHING THE HEART:
Abū al-Dardāʾ (raḍī Allāhu ʿʿʿanhu) said: “For everything there is a polish and the polish for the heart is the dhikr of Allāh.” Imām al-Bayḥaqī relates from Ibn ʿUmar (raḍī Allāhu ʿʿʿanhu) that Allāh’s Messenger (ṣallallāhu ʿalayhi wa-sallam) said: “For everything there is a polish, and the polish for the hearts is the dhikr (remembrance) of Allāh. There is nothing more potent in saving a person from the punishment of Allāh than the dhikr of Allāh.” It was said: Not even Jihād in the Path of Allāh. So he replied: “Not even if you were to continue striking with your sword until it breaks.”  There is no doubt that hearts becomes rusty just as copper and silver coins become rusty. The polish for (this rust) is the dhikr of Allāh. This is because (dhikr) is like a polish (which polishes the heart) like a shiny mirror. When dhikr is left, the rust returns. But when dhikr resumes, then the heart is (again) polished. And hearts become rusty due to two things:- [i] neglecting remembering Allāh, and [ii] committing sins. The polish for these two things is:- [i] seeking Allāh’s forgiveness and [ii] dhikr.
CONFUSING TRUTH WITH FALSEHOOD:
Whoever neglects [remembering Allāh] most of the time, then his heart will become rusty in accordance with how neglectful the person is. And when this (filthy) rust accumulates on the heart, then it no longer recognises things as they really are. Thus, it views falsehood as if it is the truth, and truth as if it is falsehood. This is because this rust darkens and confuses the heart's perception, and so it is unable to truly recognise things for what they really are. So as the rust accumulates, the heart gets blackened, and as this happens the heart becomes stained with this filthy rust, and when this occurs it corrupts the heart's perception and recognition of things. The heart (then) does not accept the truth nor does it reject falsehood, and this is the greatest calamity that can strike the heart. Being neglectful (of dhikr) and following of whims and desires is a direct consequence of such a heart, which (further) extinguish the heart's light and blinds its vision. Allāh - the Most High - said
“And do not obey him whose heart We have made to be neglectful of Our remembrance, one who follows his own whims and desires and whose affairs are furat (have gone beyond bounds and whose deeds have been lost).” [Sūrah al-Kahf 18:28]
QUALITIES OF A GUIDE:
So when a worshipper desires to follow another person, then let him see: Is this person from the people of dhikr, or from the people who are negligent (about remembering Allāh)? Does this person judge in accordance with his whims and desires, or by the Revelation? So, if he judges by whims and desires then he is actually from those people who are negligent; those whose affairs have gone beyond bounds and whose deeds are lost. The term furat (which occurs in the above verse) has been explained in many ways. It has been explained to mean:- [i] losing the rewards of that type of action which is essential to do, and in which lies success and happiness; [ii] exceeding the limits of something; [iii] being destroyed, and [iv] opposing the truth. Each of these sayings are very close in meaning to each other. The point is that Allāh - the One free from all imperfections, the Most High - has prohibited following all those who possess such attributes. So it is absolutely essential that a person considers whether such attributes are found in his shaykh, or the person who’s example he follows, or the person that he obeys. If they are, then he should distance himself from such a person. However, if it is found that the person is, in most cases, pre-occupied with the dhikr of Allāh and with following the Sunnah, and his affairs do not exceed the limits, but rather he is judicious and resolute in his affairs, then he should cling to him very firmly.
Indeed, there is no difference between the living and the dead, except with the dhikr of Allāh; since (the Prophet (ṣallallāhu ʿalayhi wa-sallam)) said: “The example of one who remembers Allāh and someone who does not, is like the example between the living and the dead.” 
 al-Waabilus-Sayyib min Kalimit-Tayyib (p. 78-82)
 Ḥasan: Related by Abū Nuʿaym in al-Hilyatul-Awliyaa‘ (5/361-362). It was authenticated by Shaykh al-Albānī in Ṣaḥīḥ al-Jāmiʿ(no. 5720).
 Ṣaḥīḥ: Related by Ibn al-Sunnī in ’Amalul-Yawm wal-Laylah (no. 3). Refer to Ṣaḥīḥ al-Jāmiʿ (no. 5446).
 Ḥasan:Related by Ibn Hibbān (no. 2318).
 Ṣaḥīḥ: Related by Aḥmad (4/352), from Muʿādh Ibn Jabal (raḍī Allāhu ʿʿʿanhu). It was authenticated by al-Albānī in Ṣaḥīḥ al-Jāmiʿ(no. 5644).
 Related by al-Bukhārī (11/208) and Muslim (1/539)