(This is) a Book (the Qur-an) which We have sent down to you, full of blessings, that they may ponder over its Verses, and that men of understanding may remember.
And hold fast, all of you together, to the Rope of Allah (i.e. this Qur-an), and be not divided among yourselves, and remember Allah’s Favour on you, for you were enemies one to another but He joined your hearts together, so that, by His Grace, you became brethren (in Islamic Faith), and you were on the brink of a pit of Fire, and He saved you from it. Thus Allah makes His Ayat (proofs, evidence, verses, lessons, signs, revelations, etc.,) clear to you, that you may be guided.
Surah (Chapter) Al-e-‘Imran (The Family of ‘Imran) 3:103
"And verily, this (i.e. Allah’s Commandments mentioned in the above two Verses 151 and 152) is My Straight Path, so follow it, and follow not (other) paths, for they will separate you away from His Path. This He has ordained for you that you may become Al-Muttaqun (the pious)."
(He has made it) straight to give warning (to the disbelievers) of a severe punishment from Him, and to give glad tidings to the believers (in the Oneness of Allah - Islamic Monotheism), who do righteous deeds, that they shall have a fair reward (i.e. Paradise).
Surah (Chapter) al-Kahf (The Cave) 18:2
18. Fasl (Conclusive) فَصْل
إِنَّهُ لَقَوْلٌ فَصْلٌ
Verily, this (the Qur-an) is the Word that separates (the Truth from falsehood, and commands strict laws for mankind to cut the roots of evil).
Surah (Chapter) at-Tariq (The Night Comer) 86:13
19. Naba" Azim (The Great News) النَّبَإِ الْعَظِيم
عَنِ النَّبَإِ الْعَظِيمِ
About the great news, (i.e. Islamic Monotheism, the Qur-an, which Prophet Muhammad صلى الله عليه وسلم brought and the Day of Resurrection).
Surah (Chapter) Naba" (The Great News) 78:2
20. Ahsan al-Hadith(The Fairest of Statements)أَحْسَنَ الْحَدِيث
Allah has sent down the Best Statement, a Book (this Qur-an), its parts resembling each other (in goodness and truth) (and) oft-repeated. The skins of those who fear their Lord shiver from it (when they recite it or hear it). Then their skin and their heart soften to the remembrance of Allah. That is the guidance of Allah. He Guides therewith whom He wills; and whomever Allah sends astray, for him there is no guide..
Surah (Chapter) az-Zumar (The Groups) 39:23
21. Tanzil (Revelation) تَنزِيل
وَإِنَّهُ لَتَنزِيلُ رَبِّ الْعَالَمِينَ
And truly, this (the Qur-an) is a revelation from the Lord of the ‘Alamin (mankind, jinn and all that exists),
And thus We have sent to you (O Muhammad صلى الله عليه وسلم) Ruh(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 Qur-an) a light wherewith We guide whosoever of Our slaves We will. And verily, you (O
Muhammad صلى اللهعليه و سلم) are indeed guiding (mankind) to the Straight Path (i.e. Allah’s Religion of Islamic Monotheism).
Surah (Chapter) ash-Shura (The Consultation) 42:52
Say (O Muhammad صلى الله عليه وسلم): "I warn you only by the Revelation (from Allah and not by the opinion of the religious scholars and others). But the deaf (who follow the religious scholars and others blindly) will not hear the call, (even) when they are warned [i.e. one should follow only the Qur-an and the Sunnah (legal ways, orders, acts of worship, and the statements of Prophet Muhammad صلى الله عليه وسلم, as the companions of the Prophet صلى الله عليه وسلم did)]
And indeed now We have conveyed the Word (this Qur-an in which is the news of everything) to them, in order that they may remember (or receive admonition).
And thus have We sent it (the Qur-an) down to be a judgment of authority in Arabic. Were you (O Muhammad صلى الله عليه وسلم) to follow their (vain) desires after the knowledge which has come to you, then you will not have any Wali(protector) or Waq (defender) against Allah.
Surah (Chapter) ar-Ra'd (The Thunder) 13:37
From The Encyclopedia of Islam by Suhel Farooq Khan