﴿ إِنَّ عَلَيْنَا جَمْعَهُۥ وَقُرْءَانَهُۥ ﴾

“for, behold, it is for Us to gather it [in thy heart,] and to cause it to be read [as it ought to be read].”

(Lo! upon Us (resteth) the putting together thereof) preserving the Qur'an in your heart (and the reading thereof) and also preserving the reading of Gabriel to you; it is also said that this means: upon Us rests its composition of the lawful and the unlawful.