وَقَالَ ٱلَّذِينَ كَفَرُواْ لَوۡلَا نُزِّلَ عَلَيۡهِ ٱلۡقُرۡءَانُ جُمۡلَةً وَٰحِدَةً ۚ كَذَٰلِكَ لِنُثَبِّتَ بِهِۦ فُؤَادَكَ ۖ وَرَتَّلۡنَٰهُ تَرۡتِيلًا
Those who reject Faith say: "Why is not the Qur'an revealed to him all at once? Thus (is it revealed), that We may strengthen thy heart thereby, and We have rehearsed it to thee in slow, well-arranged stages, gradually.<br/>
And those who disbelieve say, 'Why has Al-Qur'an not been revealed to him all at once?', as the Torah, the Bible and the Book of Psalms [were]. God, exalted be He, says: We have revealed it, thus, in parts, [it is], that We may strengthen your inner-heart with it, and We have arranged it in a specific order, that is to say, We produce it in stages one part after another, gradually and deliberately, in order to facilitate its comprehension and its memorisation.