Az-Zumar describes the Quran itself as 'the best of speech, a consistent Book, oft-repeated, from which the skins of those who fear their Lord shiver, then their skins and hearts relax at the remembrance of God' (39:23), a passage frequently cited in discussions of the physical and emotional effect skilled recitation is reported to have on listeners. Later Islamic writing on the etiquette of recitation, tajwid and its accompanying spiritual discipline, cites the verse as scriptural description of an intended, not merely incidental, response to hearing the Quran recited with attention and humility, khushu, rather than treating any emotional reaction as purely a matter of individual temperament.
Classical commentators read the sequence, shivering followed by relaxation, as tracing a movement from initial awe or fear at the Quran's warnings to eventual comfort at its promises of mercy, a pattern some exegetes read as a miniature of the Quran's overall rhetorical movement between warning and consolation across its longer surahs. The verse is regularly invoked in later devotional and even reported testimonial literature describing powerful reactions to public recitation, treated as continuous with, rather than a departure from, the response the Quran here describes as characteristic of sincere listeners.