Allah, the Wise, says:
أَلاَ بِذِکْرِ اللهِ تَطْمَئِنُّ الْقُلُوبُ
"Now surely by Allah's remembrance are the hearts set at rest." 
Allah said to Musa (a.s):
لاَ تَدَعْ ذِکرِي عَلىَ کُلِّ حاَلٍ.
"Under no circumstance (should you) abandon My remembrance." 
Remembering Allah - with concentration and presence of heart - is the ultimate objective of all acts of worship. If a dhakir (one who recites dhikr and is engaged in the remembrance of Allah) is focussed towards Allah in heart and deeds, he shall come to possess a rank such that the Satan would be unable to overcome him and gain dominance over him!
If the tongue were to recite, but the heart were to be heedless, the effects and the benefits would be reduced. At the same time if he were to regard his recitations as something very important and significant, he would be overcome by pride and vanity.
Accordingly, it is vital that in addition to remembering Allah, a person should regard himself as trivial and insignificant - rather, he should look upon himself as a non-entity before His bounties; he should beseech Him to never ever make him heedless and negligent of His remembrance but instead bestow an increase in it.
1 – Remembering Allah when Confronting the Enemy
The Noble Prophet (s.a.w) had started out for a battle and on the way ordered his army to halt.
In order to relieve himself, he distanced himself from his forces and headed towards a secluded location. In the meantime, it began to rain and it rained so hard that water began to flood as a result of which, the Noble Prophet (s.a.w) was cut off from his army.
Having witnessed the change in weather, he (s.a.w) sat beneath a tree when Huwairith Ibn al-Harith happened to see him. Speaking to his companions, he said: "This man is Muhammad and he has become isolated from his forces. May Allah kill me if I do not kill him!"
He unsheathed his sword and rushed at him (s.a.w) saying: "Who is it that can deliver you from me?" The Noble Prophet (s.a.w) said: "Allah" and then prayed softly: "O' Lord! Deliver me from the evils of Huwairith in any manner as you please."
Just as Huwairith was about to inflict his blow an angel struck him on his shoulder as a result of which he collapsed onto the ground and the sword fell from his grasp. The Noble Prophet (s.a.w) picked it up and said to him: "Who is it that can save you from me?" He said: "No one." The Noble Prophet (s.a.w) advised: "Accept Islam and I shall hand your sword back to you!" He said: "I shall not accept Islam but I shall pledge that neither shall I fight you and your followers, nor help anyone against you."
The Noble Prophet (s.a.w) returned his sword to him whereupon, Huwairith said: "I swear that you are better than me."
2 – The Enamoured One
Sadi states: "Once it so happened that I had been travelling throughout the night in the company of a group of people. Accompanying us on this journey was a person, who was obsessed with Allah and drowned in His love. It was not yet dawn when we reached a jungle where we decided to rest, however as soon as we arrived, the person uttered a cry and rushing into the woods immediately engaged himself in supplicating and communicating with his Lord.
When it was morning, I asked him: What was that state which overcame you last night? He replied: Looking into the jungle, I witnessed the nightingales on the trees, the partridges on the mountains, the frogs in the water and the various animals in the jungle weeping and lamenting (out of love for Allah), and so thought to myself that it would be contrary to courtesy and civility that while all the other creations were engaged in His glorification, I slept, heedless and unmindful of Him."
3 – The Poor Ones Question the Noble Prophet
Some of the poor persons of Madinah approached the Noble Prophet (s.a.w) and said to him: "The affluent ones perform acts of goodness like freeing slaves, giving charity, performing the Hajj etc., which are beyond our means (as a result, they shall be in possession of greater rewards than us)."
The Noble Prophet (s.a.w) said: "One, who recites Allahu Akbar a hundred times, shall be granted rewards which shall exceed the rewards of freeing one hundred slaves. One, who recites Subhan Allah a hundred times, shall come to possess rewards better than the rewards associated with the performance of Hajj. Reciting Alhamdulillah a hundred times is better than giving one hundred fully laden horses as charity in the way of Allah. One, who recites La Ilaha Illallah a hundred times, shall be of the best of the people on the Day of Judgment."
When the affluent ones of Madinah came to know of this they too began to act upon these recommendations and so the poor ones again approached the Noble Prophet (s.a.w) and complained: "The affluent ones too have started to act upon your recommendations!" Hearing their complaint, he (s.a.w) remarked: "This is Allah"s grace and favour; He grants it to whomsoever He pleases."
4 – Remembering the Beloved while in Comfort
Allah had granted immense bounties to Prophet Ayyub (a.s) such that it has been reported that he possessed five hundred pairs of bulls for ploughing his fields and hundreds of slaves, who used to cultivate his farms. His cargo-carrying camels were three thousand in number while his ship totalled seven thousand.
In addition to this, Allah had also granted him good health and numerous children. On his part, Ayyub (a.s) perpetually praised and thanked his Lord, and when faced with two acts of obedience, he would always choose the more difficult of the two.
But then, he became the object of Divine trials - not for having committed any sin but rather for raising his rank and status - such that Allah took back all the bounties that He had given him and afflicted his body with an incurable disease.
However, despite the severity of the adversity, when Ayyub (a.s) never abandoned thanking, praising and remembering Allah, the Satan got into the act. He began whispering into his (a.s) wife's mind as a result of which she started to complain of the hard times that had befallen them and would moan: "Everyone has deserted us and we do not possess anything." Ayyub (a.s) said: "For eighty years we had been receiving the bounties of Allah and so we should not complain for seven years of hardships but instead continue to remember Him in all circumstances!"
But his wife continued to complain and protest, and persistently placed before him irrational ideas till eventually, enraged, he hollered: "Go away from me such that I do not set my eyes upon you ever again."
When his wife had left him, Ayyub found himself alone and without a caretaker; going into prostration, he began praying to his Lord and communicating with Him. On this occasion Allah answered the prayers of His servant, who had continued to praise and thank Him, and once again granted him all the bounties!
Meanwhile his wife thought to herself: "Though he has driven me away, it is inappropriate for me to leave him alone. He has none to look after him and he may perish out of hunger." With this in mind she returned to the place where she had left him but found him missing, while in his place, sat a youth. As she began to weep, the youth asked her: "Why do you weep?" She replied: I had left my old husband here but I do not see him anymore. The youth said: "If you were to see him, would you recognize him?" She said: "Yes." Having answered him, she then looked at him hard and realised that he possessed a great resemblance to her husband. The youth then said to her: "I am the same Ayyub."
5 – The Woman who Remembered Allah
Sayyidah Nafisah, the daughter of Hasan Ibn Zaid Ibn Hasan al-Mujtaba (a.s)) married Ishaq Mutamin, the pious and virtuous son of Imam Jafar Sadiq (a.s). She was of the rare and distinguished ladies of her time and stood apart from the rest with regards to worship and remembrance of Allah.
Zainab, her niece, states: "I had been in the services of my aunt for forty years and throughout this period neither did I ever observe her sleep at night (for she would be engaged in worship) nor eat in the day (for she would be engaged in fasting). Once I said to her: "Would it not be better if you were to ease things upon yourself?" She replied: "How can I place myself in ease when I have before me the bottlenecks of the Purgatory and the Day of Judgment which none can cross save the delivered ones!"
She possessed great wealth, which she used to spend on the sick, the bed-ridden and the impoverished ones for the pleasure of Allah.
She had the honour of performing the Hajj on thirty occasions - most of her journeys to the House of Allah being accomplished on foot. Once, in the company of her husband, she started out from Madinah for Palestine in order to visit the grave of Prophet Ibrahim (a.s) after which she proceeded towards Egypt.
The inhabitants of Egypt requested her to settle down there and she agreed. She dug a grave in her house and perpetually engaged herself in worship and remembrance of Allah - reportedly completing thousands of recitations of the Noble Qur`an in the grave.
According to Hadith-e-Qudsi, when Allah observes that a servant of His continually engages himself in His remembrance, He manifests the person's worth amongst the people and makes him respected and revered.
In the neighbourhood of Nafisah there lived a Jew, who had a daughter who was blind. By means of the water of Nafisah's Wudhhu, the Jew's daughter regained her sight and this prompted numerous Jews of Egypt to accept Islam.
One day, in a state of fast, as she recited the chapter al-Anam of the Noble Qur`an, upon reciting the verse:
لَهُمْ دَارُ السَّلاَمِ عِنْدَ رَبِّـهِمْ
"They shall have the abode of peace with their Lord"
her soul departed from her body. The people wanted her to be buried in Egypt but her husband, desiring to take her to Madinah, refused. At night the Noble Prophet (s.a.w) appeared to him in his dream and said: "Do not oppose the people of Egypt in connection with Nafisah's burial since Allah shall descend His mercy upon them as a result of her blessed presence there."
 Suratul Ra~d (13), Verse 28
 Bihar al-Anwar, vol. 13, pg. 342
 Dastan-ha Wa Pand-ha, vol. 2, pg. 67; The commentary of Abul Futuh
 Hikayat-ha-e-Gulistan, pg. 127
 Shanidaniha-e-Tarikh, pg. 18; Mahajjatul Baidha, vol. 2, pg. 274
 Tarikh-e-Anbiya, vol. 2, pg. 20
 Shagirdan-e-Maktab-e-Aimmah, pg. 168; Wafiyyat al-ª~yan, vol. 5, pg. 56