Every limb of the human body has the capacity to engage in a brief act of worship. The remembrance of God (dhikr) is the worship of the heart and tongue, except it is not as transient. They [the heart and tongue] have been ordered to remember the Object of their worship and love in every state - standing, sitting, and lying down on their sides. For just as dhikr plows the otherwise barren fields of paradise, it nurtures and develops the desolate wrecks of our hearts.

Dhikr is what cleanses and polishes the heart; it is medicine for the heart when it falls ill. The more the worshipper increases her focus in her dhikr, the more the Remembered increases in love and yearning to meet her. If the heart is in harmony with the tongue in dhikr, it forgets everything else; and God preserves for it everything else. Dhikr itself compensates for everything. It dispels the weakness from one's hearing, the muteness from one's tongue, and the darkness from one's sight.

With it, God adorns the tongues of those who remember [Him], as He adorns with light the sight of the beholders. The heedless tongue is like the blind eye, the deaf ear, and the paralyzed hand.

Dhikr is the greatest of God's doors that remains open between Him and His servant as long as the servant does not close it with his heedlessness. Al-Hasan al-Basri, may God have mercy on his soul, said: "Seek the sweetness [of faith] in three things: in prayer, in dhikr, and in the recitation of the Qur'an. If you find it [then be it], otherwise know that the door is closed."

With dhikr, the [believing] servant prevails over Satan, while Satan prevails over those who are heedless and forgetful [of God].

Dhikr is also the soul of good deeds. Should a deed lack in dhikr, it becomes like the soul-less body.

God gave us a general order to remember [Him]:

"O you who have believed, remember Allah with much remembrance, and exalt Him morning and afternoon." Qur'an 33:41-42

He forbade us from its inverse states-heedlessness and forgetfulness:

"And remember your Lord within yourself in humility and in fear without being apparent in speech - in the mornings and the evenings; and do not be among the heedless." Qur'an 7:205

"And be not like those who forgot Allah, so He made them forget themselves. Those are the defiantly disobedient." Qur'an 59:19

He hinged success on remembering Him, much and often:

"...and remember Allah much so you may be successful." Qur'an, 8:45

He greatly praised those who are mindful and told of what He has prepared for them of Paradise and forgiveness:

"...and the men who remember Allah often and the women who do so - for them Allah has prepared forgiveness and a great reward." Qur'an 33:35

And He told us of the loss of those distracted by money and progeny:

"So remember Me, I will remember you; and be grateful to Me and do not deny Me."  Qur'an 2:152

And he told us that His Remembrance is greater than anything else:

"...and the remembrance of Allah is the greatest." Qur'an 29:45

God sealed with it good deeds, such as fasting:

"...and to glorify Allah for that which He has guided you [to]; and perhaps you will be grateful." Qur'an 2:185

And He sealed with it the pilgrimage:

"And when you have completed your rites, remember Allah like you remembered your fathers, rather with a [much] greater remembrance." Qur'an 2:200

And He sealed with it prayer:

"And when you have completed the prayer, remember Allah standing, sitting, or [lying] on your sides." Qur'an 3:103

And He sealed with it the Friday prayer:

"And when the prayer has been concluded, disperse within the land and seek from the bounty of Allah, and remember Allah often so you may succeed." Qur'an 62:10

For this reason, dhikr is the [best] ending for this life, and if it is the last of a servant's speech, God enters him into Paradise.

The mindful heart is like the living in the homes of the living, and the heedless [heart] is like the dead in the homes of the dead - for there is no doubt that the bodies of the heedless are graves for their hearts, and that the hearts within them are like the dead in their graves.

Dhikr of the tongue, in harmony with the heart, is of different kinds.

The Prophetic Dhikrs combine all three, for they include God's praise, supplication, and perfect protection [for the self and heart].

Source: SuhaibWebb - Excerpts from Madarij as-Salikeen by Ibn al-Qayyim. Abridged by Ahmed Mustafa Qasim at-Tahtawi. Translated by Huda Shaka