﴿ وَقَالَ ٱلَّذِينَ كَفَرُوا۟ لَوْلَا نُزِّلَ عَلَيْهِ ٱلْقُرْءَانُ جُمْلَةًۭ وَٰحِدَةًۭ ۚ كَذَٰلِكَ لِنُثَبِّتَ بِهِۦ فُؤَادَكَ ۖ وَرَتَّلْنَٰهُ تَرْتِيلًۭا ﴾

“Now they who are bent on denying the truth are wont to ask. “Why has not the Qur’an been bestowed on him from on high in one single re­velation?” [it has been revealed] in this manner so that We might strengthen thy heart thereby - for We have so arranged its component parts that they form one consistent whole -”

(And those who disbelieve) Abu Jahl and his host (say: Why is the Qur'an not revealed unto him all at once) just like the Torah was revealed all at once to Moses, and the Gospel to Jesus and the Psalms to David? ((It is revealed) thus) He says: We have sent Gabriel with the Qur'an in instalments (that We may strengthen thy heart therewith) that We may gladden your heart and preserve your heart; (and We have arranged it in right order) We exposited it by detailing the commands and prohibitions; it is also said that this means: We have sent Gabriel with the Qur'an in instalments verse after verse.