The Quran is a healing and a mercy to the believers
Question

Tell me more about quran.
Praise be to Allah.The Quran is the word of Allah that was revealed to His Prophet Muhammad (peace and blessings of Allah be upon him) and is recited as an act of worship.  
This definition of the Quran is comprehensive.  
Our saying “the word of Allah” excludes the words of human beings or others. 
Our saying “revealed to His Prophet Muhammad (peace and blessings of Allah be upon him)” excludes anything that was revealed to anyone else, such as the Injeel (Gospel), Tawraat (Torah) and Zaboor (Psalms). 
Our saying “it is recited as an act of worship” excludes the hadeeth qudsi (ahaadeeth in which the Prophet (peace and blessings of Allah be upon him) narrated words from Allah which are not part of the Quran). 
It brings light and gives certainty, it is the strong rope, it is the path of the righteous. It tells us of those who came before us, Prophets and righteous people, and how those who disobeyed them tasted the punishment of Allah and were humiliated. It contains verses which speak of the miracles of Allah and His power in this great universe. It tells us of the origins of human beings who are created from “despised water” (semen). It contains the basic principles of faith which must be embraced by every humble heart. It contains the rules of sharee’ah which tells us what is permissible and what is forbidden; what is true and what is false. It tells us of the Resurrection and the fate of human beings, either in the Fire in which they will burn and be among those who are humiliated, or in Paradise with its gardens, springs, plants and places of security. 
In it there is healing for men’s hearts, light and illumination for the blind. Allah says (interpretation of the meaning): 
“And We send down of the Quran that which is a healing and a mercy to those who believe (in Islamic Monotheism and act on it), and it increases the Zaalimoon (polytheists and wrongdoers) nothing but loss” [al-Isra’ 17:82]
Al-Haafiz Ibn Katheer said in his commentary on this verse: 
Here Allah tells us about His Book, which He revealed to His Messenger Muhammad (peace and blessings of Allah be upon him) and which is the Quran which “Falsehood cannot come to it from before it or behind it, (it is) sent down by the All-Wise, Worthy of all praise” [Fussilat 42:41- interpretation of the meaning], that it is “a healing and a mercy to those who believe” – i.e., it takes away the diseases in the heart such as doubt, hypocrisy, shirk, deviation and misguidance; the Quran heals all of that. And it is also a mercy which brings about faith, wisdom and the pursuit of and desire for goodness. This is only for those who believe in it and follow it; for such it will be a healing and a mercy. But as for the kaafir and those who wrong themselves thereby, their hearing the Quran only makes them further away (from truth) and increases them in kufr. The problem comes from the kaafir, not from the Quran. Allah says (interpretation of the meaning): 
“Say: It is for those who believe, a guide and a healing. And as for those who disbelieve, there is heaviness (deafness) in their ears, and it (the Quran) is blindness for them. They are those who are called from a place far away (so they neither listen nor understand)” [Fussilat 41:44]
“And whenever there comes down a Soorah, some of them (hypocrites) say: ‘Which of you has had his Faith increased by it?’ As for those who believe, it has increased their Faith, and they rejoice.
But as for those in whose hearts is a disease (of doubt, disbelief and hypocrisy), it will add suspicion and doubt to their suspicion, disbelief and doubt; and they die while they are disbelievers”
[al-Tawbah 9:124-125]
Qutaadah said, concerning the phrase “And We send down of the Quran that which is a healing and a mercy to those who believe”: when the believer hears it he benefits from it, memorizes it and understands it. “and it increases the Zaalimoon (polytheists and wrongdoers) nothing but loss” means, they do not benefit from it, memorize it or understand it. Allah has made this Quran a healing and a mercy for the believers."(Tafseer Ibn Katheer, 3/60). 
Allah says (interpretation of the meaning): 
“O mankind! There has come to you a good advice from your Lord (i.e. the Quran, enjoining all that is good and forbidding all that is evil), and a healing for that which is in your breasts, — a guidance and a mercy (explaining lawful and unlawful things) for the believers” [Yoonus 10:57] 
“And if We had sent this as a Quran in a foreign language (other than Arabic), they would have said: ‘Why are not its verses explained in detail (in our language)? What! (A Book) not in Arabic and (the Messenger) an Arab?’ Say: ‘It is for those who believe, a guide and a healing. And as for those who disbelieve, there is heaviness (deafness) in their ears, and it (the Quran) is blindness for them. They are those who are called from a place far away (so they neither listen nor understand)’” [Fussilat 41:44]
In it is guidance for mankind, away from misguidance and to the truth. Allah says (interpretation of the meaning): 
“This is the Book (the Quran), whereof there is no doubt, a guidance to those who are Al-Muttaqoon [the pious” [al-Baqarah 2:2] 
“And thus We have revealed to you (O Muhammad) a Quran in Arabic that you may warn the Mother of the Towns (Makkah) and all around it, and warn (them) of the Day of Assembling of which there is no doubt, when a party will be in Paradise (those who believed in Allah and followed what Allah’s Messenger brought them) and a party in the blazing Fire (Hell) (those who disbelieved in Allah and followed not what Allah’s Messenger brought them)” [al-Shoora 42:9] 
“And thus We have sent to you (O Muhammad) Rooh (a revelation, and a mercy) of Our Command. You knew not what is the Book, nor what is Faith? But We have made it (this Quran) a light wherewith We guide whosoever of Our slaves We will. And verily, you (O Muhammad) are indeed guiding (mankind) to the Straight Path (i.e. Allah’s religion of Islamic Monotheism).
The path of Allah to Whom belongs all that is in the heavens and all that is in the earth. Verily, all matters at the end go to Allah (for decision)” [al-Shoora 42:52-53]
It contains innumerable benefits, so everyone who seeks happiness in this world and in the Hereafter must refer to it for judgement and follow its commands.  
Imam Ibn Hazm said:
Because the proof and the miracles indicate that the Quran is the covenant of Allah with us, we must believe in it and act in accordance with it. It has come down to us through generations of Muslims narrating it to those who came after them, which leaves no room for doubt that the Quran is the one which is written in the Mus-hafs which we find everywhere. We have to follow its teachings, for it is our reference-point, because we read in it the words (interpretation of the meaning): 
“There is not a moving (living) creature on earth, nor a bird that flies with its two wings, but are communities like you. We have neglected nothing in the Book, then unto their Lord they (all) shall be gathered” [al-An’aam 6:38]
Whatever commands and prohibitions are in the Quran, we must adhere to them."(Al-Ihkaam, 1/92)
And Allah knows best.