The Quran says in Verse 23 of Surah Az-Zumar: “Allah has revealed (from time to time) the most beautiful Message in the form of a Book with similar passages which refer to each other and make the skins of those who fear their Lord shiver.”
The Arabic word used in this verse is hadith for the Quran and the phrase ‘Ahsan al-hadith’ (the best hadith) underlines the Quran’s comprehensiveness, truthfulness, firmness, and eloquence.
1- Comprehensiveness: The Quran includes everything that is needed for the guidance and growth of human beings. Also, because the Quran is the last divine book, it contains the teachings and guidance included in all previous divine books.
2- Truthfulness: Based on Verse 81 of Surah Al-Isra: “Say: ‘Truth has come and falsehood has vanished. Indeed, falsehood will certainly vanish,’” the truth will always overcome falsehood at the end. Since the Quran is the truth, and the truth is always victorious, the Quran will be victorious in every confrontation with falsehood and the light of the Quran can never be put out. “They want to put out the light of God with their mouths, but God will certainly make His light shine forever - even though the disbelievers may dislike this.” (Verse 8 of Surah Saff)
3- Firmness: The firmness of the Quran lies in the fact that it is the last divine book. There has been no alteration or distortion in it and no divine book is going to be revealed after it. So the Quran will remain firm and stable forever.
4- Eloquence: This refers to the beauty of the word of God and it being simple and at the same time profound. The Quran talks to people in such a way that everyone understands but at the same time it conveys a lofty level of knowledge and wisdom.
The word Mutashabih (similar) in the verse 23 of Surah Az-Zumar underlines that different parts of the Quran are in harmony and there are no contradictions and inconsistencies in them.
This is while in people’s speeches and words, there are differences and contradictions no matter how hard they try to avoid them.
In the Quran, there are remarkable coherence and cohesion in concepts and teachings in all verses, which is proof of the fact that it is not the word of humans.
Another word in this verse is Mathani, which means the verses and words of the Quran refer to one another, that is to say, they interpret one another.