Allah knows the cries of the beasts in the forest, the sins of the people in seclusion, the movements of the fishes in the deep seas and the rising of the water by tempestuous winds. I stand witness that Muhammad is the choice of Allah, the conveyor of His revelation and the messenger of His mercy.
Now then, I advise you to fear Allah, Who created you for the first time; towards Him is your return, with Him lies the success of your aims, at Him terminate (all) your desires, towards Him runs your path of right and He is the aim of your fears (for seeking protection). Certainly, fear of Allah is the medicine for the sickness of your hearts, sight for the blindness of your spirits, the cure for the ailments of your bodies, the rectifier of the evils of your breasts, the purifier of the pollution of your minds, the light of the darkness of your eyes, the consolation for the fear of your heart and the brightness for the gloom of your ignorance.
Therefore, make obedience to Allah the way of your life and not only your outside covering, make it your inner habit instead of only outer routine, subtle enough to enter through your ribs (up to the heart), the guide for all your affairs, the watering place for your getting down (on the Day of Judgement), the interceder for the achievement of your aims, asylum for the day of your fear, the lamp of the interior of your graves, company for your long loneliness, and deliverance from the troubles of your abodes. Certainly, obedience to Allah is a protection against encircling calamities. expected dangers and the flames of burning fires.
Therefore, whoever entertains fear of Allah, troubles remain away from him after having been near, affairs become sweet after their bitterness, waves (of troubles) recede from him after having crowded over him, difficulties become easy for him after occurring, generosity rains fast over him after there had been famine, mercy bends over him after it had been loath, the favours (of Allah) spring forth on him after they had been dried, and blessing descends over him in showers after being scanty. So, fear Allah Who benefits you with His good advice, preaches to you through His Messenger, and obliges you with His favours. Devote yourselves to His worship, and acquit yourselves of the obligation of obeying Him.
This Islam is the religion which Allah has chosen for Himself, developed it before His eyes, preferred it as the best among His creations, established its pillars on His love. He has disgraced other religions by giving honour to it. He has humiliated all communities before its sublimity; He has humbled its enemies with His kindness and made its opponents lonely by according it His support. He has smashed the pillars of misguidance with its columns. He has quenched the thirst of the thirsty from its cisterns, and filled the cisterns through those who draw its water.
He made Islam such that its constituent parts cannot break, its links cannot separate, its construction cannot fall, its columns cannot decay, its plant cannot be uprooted, its time does not end, its laws do not expire, its twigs cannot be cut, its parts do not become narrow, its ease does not change into difficulty, its clarity is not affected by gloom, its straightness does not acquire curvature, its wood has no crookedness, its vast paths have no narrowness, its lamp knows no putting off and its sweetness has no bitterness.
It consists of columns whose bases Allah has fixed in truthfulness and whose foundation He has strengthened, and of sources whose streams are ever full of water and of lamps, whose flames are full of light, and of beacons with whose help travellers get guidance, and of signs through which a way is found to its highways and of watering places which provide water to those who come to them. Allah has placed in Islam the height of His pleasure, the pinnacle of His pillars and the prominence of His obedience. Before Allah, therefore, its columns are strong, its construction is lofty, its proofs are bright, its fires are aflame, its authority is strong, its beacons are high and its destruction is difficult. You should therefore honour it, follow it, fulfil its obligations and accord the position due to it.
Then, Allah, the Glorified, deputed Muhammad - the peace and blessing of Allah be upon him and his descendants - with truth at a time when the destruction of the world was near and the next life was at hand, when its brightness was turning into gloom after shining, it had become troublesome for its inhabitants, its surface had become rough, and its decay had approached near. This was during the exhaustion of its life at the approach of signs (of its decay), the ruin of its inhabitants, the breaking of its links, the dispersal of its affairs, the decay of its signs, the divulging of its secret matters and the shortening of its length. Allah made him responsible for conveying His message and (a means of) honour for his people, a period of bloom for the men of his days, a source of dignity for the supporters and an honour for his helpers.
Then, Allah sent to him the Book as a light whose flames cannot be extinguished, a lamp whose gleam does not die, a sea whose depth cannot be sounded, a way whose direction does not mislead, a ray whose light does not darken, a separator (of good from evil) whose arguments do not weaken, a clarifier whose foundations cannot be dismantled, a cure which leaves no apprehension for disease, an honour whose supporters are not defeated, and a truth whose helpers are not abandoned. 
Therefore, it is the mine of belief and its centre, the source of knowledge and its oceans, the plantation of justice and its pools, the foundation stone of Islam and its construction, the valleys of truth and its plains, an ocean which those who draw water cannot empty, springs which those who draw water cannot dry up, a watering place which those who come to take water cannot exhaust, a staging place in moving towards which travellers do not get lost, signs which no wayfarer fails to see and a highland which those who approach it cannot surpass it.
Allah has made it a quencher of the thirst of the learned, a bloom for the hearts of religious jurists, a highway for the ways of the righteous, a cure after which there is no ailment, an effulgence with which there is no darkness, a rope whose grip is strong, a stronghold whose top is invulnerable, an honour for him who loves it, a peace for him who enters it, a guidance for him who follows it, an excuse for him who adopts it, an argument for him who argues with it, a witness for him who quarrels with it, a success for him who argues with it, a carrier of burden for him who seeks the way, a shield for him who arms himself (against misguidance), a knowledge for him who listens carefully, worthy story for him who relates it and a final verdict of him who passes judgements.
(1) Al-Harrani, Tuhaf, 126;
(2) al-Kulayni, Usul al-Kafi, II, 49;
(3) al-Qali, al-'Amali, 171;
(4) Abu Talib al-Makki, Qut, I, 382;
(6) al-Saduq, al-Khisal, I, 108.