Surah Az-Zumar 39:23

ٱللَّهُ نَزَّلَ أَحْسَنَ ٱلْحَدِيثِ كِتَـٰبًا مُّتَشَـٰبِهًا مَّثَانِىَ تَقْشَعِرُّ مِنْهُ جُلُودُ ٱلَّذِينَ يَخْشَوْنَ رَبَّهُمْ ثُمَّ تَلِينُ جُلُودُهُمْ وَقُلُوبُهُمْ إِلَىٰ ذِكْرِ ٱللَّهِ ۚ ذَٰلِكَ هُدَى ٱللَّهِ يَهْدِى بِهِۦ مَن يَشَآءُ ۚ وَمَن يُضْلِلِ ٱللَّهُ فَمَا لَهُۥ مِنْ هَادٍ

Allāh has sent down the best statement: a consistent Book wherein is reiteration. The skins shiver therefrom of those who fear their Lord; then their skins and their hearts relax at the remembrance [i.e., mention] of Allāh. That is the guidance of Allāh by which He guides whom He wills. And one whom Allāh sends astray - for him there is no guide.

Translation: Saheeh International

Tafsir

God has revealed the best of discourses a Book kitāban substitutes for ahsana ‘the best’ namely a Qur’ān consimilar in other words some of its parts are similar to others in terms of their arrangement and otherwise in coupled phrases — a Book in which the Promise of reward is coupled with the Threat of punishment …

Excerpt from Tafsir al-Jalalayn, commentary on 39:23, via Quran.com. The reader has the full commentary and 9 more tafsirs.