Allaah سبحانه و تعالى says,
"This is the Book, concerning which there is no doubt. A guidance for the Muttaqeen."  (Sooratul-Baqarah, 2:2)
In the typical translation of this verse, it seems not to say a great deal about the Qur'aan. In reality, though, in this verse, Allaah سبحانه و تعالى has stated many important points about this Book. 
The first aspect that one notes is that Allaah سبحانه و تعالى refers to the Book with the demonstrative pronoun ذلك [dhaalika], which would normally be translated as, "that" instead of "this." However, the word "that" is used for "this" for particular reasons.
'Abdul Hameed Siddiqi noted, "The demonstrative pronoun ذلك [dhaalika] ["that"] indicates remoteness of distance, but at times it indicates esteem, honour and grandeur of that for which it is used as we find in the case of the Qur'aan." 
Second, the phrase is actually more comparable to something like, "This is the Book." It implies that it is the most complete book and that no other book deserves to be called a "book" like this Book does. It is the real Book that encompasses what no other previous book encompasses. In other words, Allaah سبحانه و تعالى is pointing to the completeness and perfection of this Book and, hence, its superiority over all other books. 
Third, Allaah سبحانه و تعالى mentions that this is a Book concerning which there can be no doubt. It is the case that many disbelievers and skeptics doubt this Book. However, that is not the meaning of this verse. The meaning is that the proofs and evidences that this is a true and perfect revelation from Allaah سبحانه و تعالى are so great and clear that there is in reality no room or reason for anyone to doubt this Book. This applies to the Book as a whole and every portion of its guidance. There should be no doubt concerning anything that Allaah سبحانه و تعالى has stated in this Book. The absence of doubt, as Imaam as-Sa'di رحمه الله points out, implies that the believer must be completely certain and satisfied that everything stated in this Book is true. 
Fourth, Allaah سبحانه و تعالى describes this Book as "guidance." Commenting on this portion of the aayah, Imaam as-Sa'di رحمه الله noted, "Allaah سبحانه و تعالى stated the word "guidance" without stating its regimen or governing word. He did not say, "Guidance for the benefit of so and so," or "for the benefit of such and such purpose." [Such was not said] so that the concept of guidance may be left in its generality. It is guidance for all of the needs and benefits of the life of this world and that of the Hereafter. It is the guide for humans concerning fundamental and secondary aspects. It distinguishes truth from falsehood and what is sound from what is weak. And it makes clear for them how to follow the path that is beneficial for them in both their worldly affairs and their other worldly matters. 
This verse makes it clear that the Qur'aan is first and foremost a Book of guidance.
Finally, in this verse, Allaah سبحانه و تعالى mentions that the Book is a guidance for those who have taqwa (fear of Allaah and God-consciousnes). 
Elsewhere Allaah سبحانه و تعالى has described this revelation as,
"a guidance for mankind and clear proofs for the guidance and the criterion [between right and wrong]." (Sooratul-Baqarah, 2:185)
What these two verses, Sooratul-Baqarah - 2:2 and 2:185, imply is that the guidance of the Qur'aan is there for everyone to see and benefit from. However, not everyone is going to benefit from its wonderful guidance. Only those who approach the Qur'aan in the proper way, seeking to obey it and implement its guidance, will be the ones who truly benefit from the guidance of the Qur'aan. 
 Throughout the Qur'aan, there are two words that are used quite often as a reference to the Qur'aan: the Qur'aan and the Book (Kitaab). The word "the Qur'aan" is a verbal noun implying, "the reading or the recital." This implies that the Qur'aan is something that is recited by the tongue. The word "the Book" implies that it is recorded. Muhammad 'Abdullaah Daraaz notes that these two words used for the Qur'aan imply how the Qur'aan was and is to be preserved. It was and is used to be preserved in the hearts as well as in written form. If a mistake creeps into one of these two forms, it can be spotted and corrected by the other form. This is, in reality, how the Qur'aan has been passed on throughout the centuries. Thus, there is no room for anyone to doubt the authenticity and purity of the Qur'aan.
Daraaz goes on to make another point about these two words used for the Qur'aan. Both of these words come from roots that imply, "combining or joining something together." In the case of reciting, one joints the different letters together to pronounce the proper sounds that make up the words. In the case of writing something down, one also joins the different letters together to record the proper words.
Daraaz then states that one can make the following conclusion: These words of the Qur'aan combine together all of the meanings, knowledge and truths that one needs to live. This conclusion is supported by what Allaah Himself سبحانه و تعالى has said about the Qur'aan,
"And We have sent down to you the Book (the Qur'aan) as an exposition of everything, a guidance, a mercy, and glad tidings for those who have submitted themselves (to Allaah as Muslims)." (Sooratun-Nahl, 16:89)
See Muhammad 'Abdullaah Daraaz, An-Naba al-'Adheem: Nadharaat Jadeedah fil-Qur'aan (Riyaadh: Daar Taibah, 1997), pp. 5-6.
Long before Daraaz, Imaam Raaghib al-Isfahaani رحمه الله made the same point concerning why this revelation is called the "Qur'aan" in comparison with the previous revelations; it encompasses all that the previous scriptures encompassed as well as all the knowledge necessary for mankind. See Imaam Raaghib al-Isfahaani رحمه الله, Mu'jam Mufradaat Alfaadh al-Qur'aan (Beirut: Daar al-Fikr, n.d.), p. 414.
 One will note that in many cases the true or complete ramifications of the original Arabic of the Qur'aan are very difficult or impossible to capture in a mere translation. Of course, the English translation cannot be called the Qur'aan. The Qur'aan is only the original Arabic text. No matter how excellent a translation may be, it can never match the miraculous nature and linguistic excellence of the Qur'aan.
 'Abdul Hameed Siddiqi, The Holy Qur'aan: English Translation and Explanatory Notes (Lahore, Pakistan: Islamic Book Centre, n.d.), vol. 1, p. 10.
There are some commentators who understand the demonstrative pronoun phrase here to mean, "that is the book." They are then forced to explain what is the referent of "that." Imaam Fakhr ad-Deen ar-Raazi رحمه الله has given seven possible explanations [see At-Tafseer al-Kabeer (Beirut: Daar Ihyaa at-Turaath al-Arabi, n.d.), vol. 2, pp. 12-13.]. However, it is clear from the statements of the Companions رضي الله عنهم that the meaning of the phrase is "this is the book" and not "that is the book."
 Imaam 'Abdur Rahmaan as-Sa'di رحمه الله, Taiseer al-Kareem ar-Rahmaan fee Tafseer Kalaam al-Mannaan (Beirut: Muassasah ar-Risaalah, 1996), p. 23.
 How to Approach and Understand the Qur'aan, pp. 8-11.