There is no question that the Qur'aan guides to the straight path and to the truth. This is one of its major goals. Yet, at the same time, although this guidance is perfect and preserved, it must be allowed to guide the reader. The Qur'aan must be given the opportunity to tell its reader what the straight path is. That is, the reader must approach the Qur'aan with, if one may use the expression, an "open mind." If the reader has already decided what is right and what is wrong, and is only looking to the Qur'aan to substantiate his views, then the Qur'aan will never give him the guidance it contains. Indeed, in that case, the Qur'aan would never be given that opportunity.
Unfortunately, it is the case with some readers of the Qur'aan who, instead of letting the Qur'aan speak for itself, have taken it upon themselves to speak for the Qur'aan. If it contains any passage that contradicts their preconceived notions of what is the truth, instead of accepting what the Qur'aan says, they simply try to reinterpret the Qur'aan in such a way that it is consistent with their beliefs and ideas. They do not realise that it is their thinking and beliefs that need to be changed or corrected according to the Qu'raan and not vice-versa. Allaah سبحانه و تعالى, Who revealed the Qur'aan, is not in need of their far-fetched interpretations. It (along with the Sunnah of the Prophet Muhammad صلى الله عليه وسلم of course) presents the truth in clear and plain language and it is simply up to the reader to accept what Allaah سبحانه و تعالى has said in the Qur'aan.
In the history of Islaam, one can see that the lack of allowing the Qur'aan to state what is true and what is false has been a major characteristic of the heretical and stray groups (ahlul-bida'). 
They approached the Qur'aan with preconceived notions and tried to force their opinions on the Qur'aan. 
Without a doubt, it can be stated that they did not turn to the Qur'aan for its guidance - since they had already decided what the truth is. They turned to it only trying to substantiate their views. A glaring example of this nature is the Mu'tazilah  who even attempted to change the wording of the Qur'aan because it was inconsistent with their preconceived beliefs. The Mu'tazilah, due to the supposedly "ingenious" theories they developed, did not believe in Allaah's سبحانه و تعالى attribute of speech. They have a length theory and proof that such an attribute is impossible for Allaah سبحانه و تعالى according according to their notion of Allaah. 
Abu Salamah  رحمه الله reported that he used to have dreams that made him ill (from fear or worry) - until he heard Abu Qatadah رضي الله عنه mention that he had the same problem, so Allaah's Messenger صلى الله عليه وسلم told him: "A pleasant (or good, or truthful) dream is from Allaah, and a bad dream is from Shaytaan. When one of you has a good dream (that he likes), let him expect good, and avoid relating it except to those whom he loves. And when he has a dream and dislikes any part of it, let him seek Allaah's protection from its evil and from Shaytaan's evil, and let him lightly spit - three times - on his left side, and avoid relating it to anyone. Indeed, it will then not harm him." 
Abu Sa'eed al-Khudri رضي الله عنه reported that he heard the Prophet صلى الله عليه وسلم say: "When one of you has a dream that he likes - indeed, it is only from Allaah, so let him praise Allaah for it and relate it (to his beloved ones). And if one of you has a dream that he hates - indeed, it is only from Shaytaan, so let him seek Allaah's protection from its evil, and let him not mention it to anyone: it will then not harm him." 
Abu Hurayrah رضي الله عنه reported that the Prophet صلى الله عليه وسلم said: "Dreams are of three categories: a good dream that has glad tidings from Allaah, a terrifying dream from Shaytaan, and a dream about what concerns a person. When one of you has a dream that he dislikes, let him rise from his sleep and pray, and let him not relate it to other people." 
A Commentary of the Hadeeth: "You are unto me as Haaroon was unto Moosaa."
On the authrority of Sa'd Ibn Abi Waqqaas رضي الله عنه, that the Messenger of Allaah صلى الله عليه وسلم said to 'Ali Ibn Abi Taalib رضي الله عنه: "You are unto me as Haaroon was unto Moosaa, except that there will be no Prophet after me." 
The narration of Ahmad on the authority of Sa'eed Ibn al-Musayyib has it that 'Ali رضي الله عنه replied: "I am content, I am content!"
Ibn Sa'd narrates essentially the same story on the authority of al-Baraa' رضي الله عنه and Zayd Ibn Arqam رضي الله عنه, who reported that 'Ali's رضي الله عنه reply was, "Indeed, O Messenger of Allaah,' to which the Prophet صلى الله عليه وسلم said, "It is indeed so."
Different ahaadeeth of the Prophet صلى الله عليه وسلم describe specific portions of the Qur'aan as having the ability to protect its Muslim reader from certain types of evil.
For example, in a hadeeth in Saheeh al-Bukhaaree, it states that a shaytaan (devil) told Abu Hurayrah رضي الله عنه, "When you go to your bed, recite the verse of the throne (Aayatul-Kursee - 2:255). If you do so, a guardian from Allaah will come and protect you from the devils until the morning." Later, the Prophet صلى الله عليه وسلم told Abu Hurayrah رضي الله عنه about that statement, "He [that devil] has told the truth although he is a liar."
The Messenger of Allaah صلى الله عليه وسلم also said, "Do not turn your houses into graves. Verily, Shaytaan flees from a house in which Sooratul-Baqarah is recited." 
There is no question that this is a true characteristic of the Qur'aan. The Muslim, though, has to realise that the Qur'aan is supposed to be a protection from a much greater evil: the Hellfire. But it will not protect one from the Hellfire unless one believes in it sincerely and applies it correctly.
Again, if a person simply turns to the Qur'aan and reads portions of it thinking that it will protect him from some evil in this life, and he does not go beyond that to understand and apply the Qur'aan properly, then he will be missing the real point of what the Qur'aan is all about. 
The Prophet صلى الله عليه وسلم has made it clear that this Qur'aan is a great blessing and miracle from Allaah سبحانه و تعالى. In the following hadeeth, the Prophet صلى الله عليه وسلم is referring to the miracles that were given to the previous Prophets عليهم الصلاة والسلام. Although the miracles that were performed at their hands were something great, they cannot compare to what the Prophet Muhammad صلى الله عليه وسلم received as his standing miracle - even the staff that was given to Prophet Moosaa (Moses) عليه السلام or the raising of the dead and healing of the blind by Prophet 'Eesaa (Jesus) عليه السلام cannot compare to what the Prophet Muhammad صلى الله عليه وسلم received in the form of the Qur'aan. For this reason, the Prophet صلى الله عليه وسلم had reason to hope that he will have the greatest number of followers on the Day of Judgement. The Prophet صلى الله عليه وسلم said, "There was no prophet among the prophets except that he was given something that would make the people believe in him. But what I have been given is an inspiration that Allaah has revealed to me. So I hope that I will have more followers than them on the Day of Resurrection." 
On the authority of Sayyiduna Abu Huraira رضي الله عنه who said: "The Messenger of Allah صلى الله عليه وسلم said, 'Verily Allaah, the Exalted, is pure and accepts only that which is pure. Allaah has commanded the believers to do that which He has commanded the Messengers. The Exalted has said, "O Messengers! Eat of the good things and do righteous deeds." And the Exalted also said, "O believers! Eat of the good things that We have provided for you."' Then he [the Prophet (peace be upon him)] mentioned a man who after a long journey is disheveled and dust-colored. '[The man] stretches his hands out toward the sky and says, "O Lord, O Lord," while his food is unlawful, his drink is unlawful, his clothing is unlawful and his nourishment is unlawful. How is he to be answered [in such a state]?'" 
Imaam at-Tirmidhi رحمه الله often uses the term hasan saheeh to describe a hadeeth. This term has led to some confusion among the scholars. However, before getting to that term, one must first define the terms saheeh and hasan. In general, for a hadeeth to be called saheeh it must meet the following five conditions: (i) The chain or isnaad must be connected, with no missing links.
The sunnah is the reality or the actual statement, act or tacit approval of the Prophet صلى الله عليه وسلم - what he actually did, said or approved of. There is no such thing as a "weak sunnah" or a "rejected sunnah." However, that actual sunnah is captured in the reports that have come down from the Prophet صلى الله عليه وسلم, which constitute the hadeeth literature. As noted before, not every report is correct and substantiated - indeed, some reports are even blatant fabrications. In other words, the entire hadeeth literature does not represent the sunnah of the Prophet صلى الله عليه وسلم. Only the acceptable ahaadeeth represent and portray the real sunnah of the Messenger of Allaah صلى الله عليه وسلم. Shaykh Ibn Taymiyyah رحمه الله wrote, for example, "The sunnah that is a must to be followed, for which one is praised upon following it and blamed for going against it, is the sunnah of the Messenger of Allaah صلى الله عليه وسلم in matters of beliefs, matters of worship and the rest of the affairs of the religion. And that is known only by knowledge of the ahaadeeth of the Prophet صلى الله عليه وسلم that are confirmed on his authority."  Once the role and the importance of the Sunnah in Islaam is made clear, the importance of the ahaadeeth should be very obvious. One needs to know what the sunnah of the Prophet صلى الله عليه وسلم was. One also needs to know where to look to find the statements of the Prophet صلى الله عليه وسلم. By the grace of Allaah سبحانه وتعالى, unlike the Messengers عليهم الصلاة والسلام who preceded the Prophet Muhammad صلى الله عليه وسلم, Allaah سبحانه وتعالى has preserved for Muslims the actual statements and actions of His last Prophet صلى الله عليه وسلم. The Prophet's صلى الله عليه وسلم statements, actions and even his physical appearance are all captured in the hadeeth literature. Virtually nothing has been lost from his noble life. A Muslim can know exactly how he prayed, fasted and participated in daily matters with his fellow companions رضي الله عنهم or with his wives رضى الله عنهنّ. Such a miraculous and complete record cannot be found for any other historical figure since the creation of man. And this is actually another sign of the truth of his Prophethood, and of the fact that he is the final prophet, after whom no prophet is needed.