Allah, the Wise, has said:
ياَ اَيُّهاَ الَّذِينَ آَمَنُوا آَمِنُوا بِاللهِ وَ رَسُولِهِ وِ الْكِتاَب
"O' You who believe! Believe in Allah and His Messenger and the Book, which He has revealed to His Messenger" 
The Holy Prophet (s.a.w.) said:
اَلإيماَنُ عَقْدٌ بِالْقَلْبِ وَ نُطْقٌ بِالْلِساَنِ وَ عَمَلٌ بِالأرْكاَن
"Faith is (a combination of) conviction in the heart, speaking out by the tongue and deeds by the limbs." 
The believers are ranked according to their level of faith. Faith has four pillars - tawakkul, tafweedh, ridha and tasleem - and one who possesses these pillars, acquires tranquillity and repose, and his faith attains stability and permanence. The faith of those who are weak in belief is neither stable nor permanent.
Did not Imam Sadiq (a.s.) say: (Allah grants the world to His friends and foes alike, but faith, He bestows only to the chosen ones from amongst His creations)?
Hence, those possessing true and perfect faith have always been in the minority; forbearance being their ‘minister' and wisdom, the ‘commander of their army'.
1 – Harithah's Martyrdom
One day, after offering the morning prayers in congregation, the Holy Prophet (s.a.w.) looked around the mosque and his eyes fell upon a youth, Harithah Ibn Maalik Ansaari, who sat with his head lowered in a state of drowsiness. His face was pale, his body thin and weak and his eyes appeared to have sunk into their sockets. The Holy Prophet (s.a.w.) approached Harithah and inquired:
"What state are you in?"
"I find myself as a true believer," replied the youth.
The Holy Prophet (s.a.w.) asked, "Everything possesses a truth; what is the truth behind what you claim?"
"O' Prophet of Allah! I have become disenchanted with the world," he answered. "I stay awake (in worship) in the night, and endure thirst (by observing fasts) in the day. It is as if I am witnessing the A'rsh (Throne) of God and the scenario of Reckoning, observing the inmates of Paradise meeting each other and hearing the shrieks of the inmates of hell."
The Holy Prophet (s.a.w.) remarked, "This is a person, whose heart Allah has illuminated". Then, addressing Harithah, he continued, "You have acquired perception and insight, so remain steadfast".
Harithah beseeched: "O' Prophet of Allah! Request Allah to grant me martyrdom while fighting alongside you!"
The Prophet prayed to Allah to grant martyrdom to Harithah. A few days later, he dispatched an army for battle and Harithah was included in it. During the battle, Harithah killed nine infidels before he himself was killed, being the tenth soldier from the Muslim force to taste the nectar of martyrdom.
2 – Who is a Youth?
Imam Sadiq (a.s.) once asked the students and companions who had gathered around him:
"Who is a ‘youth?"
A person answered, "Someone who is young in age."
The Imam (a.s.) said, "Despite the old age of the People of the Cave, on account of the faith which they possessed, God has referred to them as ‘youths'. In verse 10 of the chapter al-Kahf, He says: When the youths sought refuge in the cave.
He then continued, "Whoever believes in God and observes piety is a youth."
3 – Levels of Faith
Imam Sadiq, (a.s.) addressing a saddler, who used to serve him, said:
"Some Muslims possess one portion of faith, while there are others, who possess two or three or even seven portions of it. It is inappropriate to burden a person, possessing one portion of faith, with acts suitable for a person possessing two portions of faith. Similarly, it is inappropriate to burden a person who has two portions of faith with acts suitable for a person with three portions of faith."
The Imam (a.s.) continued, "Let me present an example:
Once, there was a man whose neighbour was a Christian. The man invited him to Islam and the Christian agreed and converted to a Muslim.
The next day at dawn, the Muslim knocked on the door of the convert's house. When the convert answered the door, the man told him to perform wudhu, get dressed and accompany him to the mosque for prayers. The neighbour duly obliged and both men proceeded to the mosque. They offered not only morning prayers but also many other prayers until it was sunrise.
The new Muslim wished to return home, when the man asked him:
‘Where are you going? The days are short and very soon it will be time for the Dhuhr prayers. Let us wait until we have offered our Dhuhr prayers.'
So they waited till it was Dhuhr, when they offered their prayer. The convert prepared to leave but the man persuaded him to stay until A'sr time. They offered A'sr prayer after which the convert decided to go. The man told him that it was almost sunset and that they should not go before offering Maghrib prayer. He then persuaded his neighbour to stay for the E'sha prayer also.
Finally, they went back home.
The next dawn, the man again knocked on the door of the convert and asked him to go to the mosque with him.
The newly converted Muslim retorted, ‘For this religion of yours, seek someone who has more time on his hands than me. I am a poor person and have a family to feed and look after!'
The Imam (a.s.) concluded, "The ignorant Muslim reverted him to his original faith of Christianity."
4 – The Faith of Sa'eed Ibn Jubair
Sa'eed Ibn Jubair was one of the steadfast and loyal companions of Imam Sajjad (a.s.). Hajjaaj was a bloodthirsty tyrant who had ruled over Kufah, Iraq and Iran for almost twenty years after being appointed by the Bani Umayyah and Bani Marwaan. He had killed nearly one hundred and twenty thousand people during his reign, and amongst the friends and descendants of A'li (a.s.) murdered by him, were individuals like Kumail Ibn Ziyaad, Qanbar, the slave of A'li, (a.s.) and Sa'eed Ibn Jubair.
Hajjaaj ordered Sa'eed to be arrested when he became aware of Sa'eed's belief and inclination towards Imam Ali (a.s.).
Initially, Sa'eed fled to Isfahan, but when Hajjaaj came to know of this, he wrote to the governor of Isfahan, seeking his arrest. The governor possessed a high regard for Sa'eed and therefore advised him to leave Isfahan for a safer resort.
Acting upon this advice, Sa'eed set out towards Qum and then proceeded to Azerbaijan and then to Iraq where he sought to enter the army of A'bd al-Rahmaan Ibn Muhammad, who had initiated a rebellion against Hajjaaj.
A'bd al-Rahmaan was defeated and Sa'eed fled to Makkah where he lived in hiding.
During that period, Makkah was under the rule of Khaalid Ibn A'bdullah Qasri, a ruthless individual, who had been placed there by the Caliph, Waleed Ibn A'bd al-Malik. Waleed wrote to him and gave him the order to arrest the well-known Iraqi personalities who were hiding in Makkah, and to send them to Hajjaj.
Thus, he arrested Sa'eed and had him dispatched to Kufah. At that time, Hajjaaj was in Waasit, a city near Baghdad, where Sa'eed was eventually brought.
Hajjaaj questioned him about himself, the Holy Prophet (s.a.w.), A'li (a.s.), Abu Bakr, U'mar, Uthmaan and many others and then asked him:
"How should I put you to death?"
"Whatever manner you may adopt to kill me, you are bound to be chastised accordingly, on the Day of Judgment," replied Sa'eed.
"I would like to forgive you."
"If the forgiveness is from God, then I seek it, but if it is from you, then I do not desire it," responded Sa'eed.
Hajjaaj ordered the executioner to sever Sa'eed's head before him. Despite his hands being tied behind his back, Sa'eed recited the following verse of the holy Qur'an:
Surely I have turned myself, wholly to Him, Who originated the heavens and the earth, being upright, and I am not of the associators.
Hearing this, Hajjaaj ordered his face to be turned away from the Qiblah, whereupon he recited the following verse:
Whithersoever ye turn, there is the presence of Allah
When Hajjaaj heard this, he ordered his men to place Sa'eed's face down, upon the ground. When this was done, Sa'eed recited the following verse:
From the (earth) did We create you, and into it shall We return you, and from it shall We bring you out once again
Hajjaaj shouted, "Don't waste any more time! Kill him!"
Sa'eed testified to the Unity of God and the Prophethood of the Holy Prophet (s.a.w.) and prayed: O' God! Do not grant Hajjaaj respite after me in order that he does not kill anyone else. As he uttered these words, the executioner severed his head.
After the martyrdom of this epitome of perfect faith, Hajjaaj suffered a derangement of his senses and did not live for more than fifteen nights. Before his death, he would occasionally lose consciousness, but regaining it, he would repeatedly mutter:
"Why did I ever get involved with Sa'eed Ibn Jubair?"
5 – Salman Farsi's Rank
Faith has ten ranks and Salman Farsi was on its tenth rank. He possessed knowledge of the unseen, the ability to interpret dreams and misfortunes, was well versed in genealogy and had even been favoured with gifts of Paradise, in this world. The Holy Prophet (s.a.w.) said: "Whenever Jibraeel would descend, he would, on behalf of God, say: Convey my salutation to Salman!"
Here is an example of the high degree of Salman's faith. Once, Abu Dharr paid Salman a visit. Salman had placed a utensil over the fire to heat its contents. The two men sat together for some time, talking to each other, when suddenly the vessel toppled over, but to Abu Dharr's amazement, its contents did not spill. Salman, picking the utensil up, placed it back upon the fire. A little later, the vessel fell over again, but once again its contents did not spill. Again Salman picked it up and placed the vessel upright.
Amazed, Abu Dharr hurried out of Salman's house and was lost in contemplation over what he had witnessed. He happened to come across Amirul Mu'mineen (a.s.) on the way and narrated the incident to him.
Having heard Abu Dharr's narration, the Imam (a.s.) said:
"If Salman were to inform you of all that he possesses knowledge of, you would surely say: ‘May God have mercy upon the murderer of Salman.' O' Abu Dharr! Salman is the ‘door' of God upon the earth. One, who recognises his status, is a Mu'min while one, who rejects him, is an infidel. Salman is (one) of us, Ahlul Bayt."
 Holy Qur'an, ch. Al-Nisaa (4), vs. 136.
 Bihaar al-Anwaar vol. 69, pg. 69.
 Relying on God. (Translator's comments)
 Entrusting one's affairs to God. (Translator's comments)
 Satisfaction and pleasure over Divine decree. (Translator's comments)
 Submission to God. (Translator's comments)
 Al-Kafi, vol. 2, ch.: The Chapter of Reality of Faith, tr. 2 & 3.
اِذ آوَى الفَتْيَةُ اِلىَ الْكَهْفِ
مَنْ آمَنَ بِاللهِ وَ اتَّقَى فَهُوَ الْفَتى
 Hikaayat-ha-e-Shanidani, vol. 5, pg. 58; Tafsir Nur al-Thaqalain, vol. 3, pg. 244.
 Namunah-e-Ma'arif, vol. 2, pg. 479; Al-Kafi, ‘The chapter of Levels of Faith', tr. 2.
 Holy Qur'an, ch. Al-Ana'am (6), vs. 79. إِنِّي وَجَّهْتُ وَجْهِيَ لِلَّذِي فَطَرَ السَّماواتِ وَ الْأَرْضَ حَنِيفاً وَ ما أَنَا مِنَ الْمُشْرِكِينَ
 Ibid, ch. Al-Baqarah (2), vs. 115. فَأَيْنَما تُوَلُّوا فَثَمَّ وَجْهُ اللَّهِ
 Ibid, ch. Taha (20), vs. 55. مِنْها خَلَقْناكُمْ وَ فِيها نُعِيدُكُمْ وَ مِنْها نُخْرِجُكُمْ تارَةً أُخْرى
 Daastaan-ha-e-Maa, vol. 2, pgs. 39-45.
 Muntahal Aa'maal, vol. 1, pg. 114.