This is Allah teaching His Messenger how to receive the revelation from the angel. For verily, he (the Prophet ) was rushing in his attempts to grasp the revelation and he would be reciting the revelation with the angel while he was reciting it. Therefore, Allah commanded him that when the angel brings some revelation to him he should just listen. Allah would make sure to collect it in his chest, and He would make it easy for him to recite it in the same way that it was revealed to him. Allah would explain it, interpret it and clarify it for him. So the first phase was gathering it in his chest, the second phase was recitation and the third phase was its explanation and clarification of its meaning. Thus, Allah says,

[لاَ تُحَرِّكْ بِهِ لِسَانَكَ لِتَعْجَلَ بِهِ ]

(Move not your tongue concerning to make haste therewith.) meaning, with the Qur'an. This is as Allah says,

[وَلاَ تَعْجَلْ بِالْقُرْءانِ مِن قَبْلِ إَن يُقْضَى إِلَيْكَ وَحْيُهُ وَقُل رَّبِّ زِدْنِى عِلْماً]

(And be not in haste with the Qur'an before its revelation is completed to you, and say: "My Lord! Increase me in knowledge.'') (20:114) Then Allah says,

[إِنَّ عَلَيْنَا جَمْعَهُ]

(It is for Us to collect it) meaning, `in your chest.'

[وَقُرْءَانَهُ]

(and that it be recited.) meaning, `that you recite it.'

[فَإِذَا قَرَأْنَـهُ]

(And when We have recited it to you,) meaning, `when the angel has recited it to you from Allah,'

[فَاتَّبِعْ قُرْءَانَهُ]

(then follow its recitation.) meaning, `listen to it then recite it as he taught you to recite it.'

[ثُمَّ إِنَّ عَلَيْنَا بَيَانَهُ ]

(Then it is for Us to make it clear.) meaning, `after memorizing it and reciting it, We will explain it to you, clarify it and inspire you with its meaning according to what We intended and legislated.' Imam Ahmad recorded from Ibn `Abbas that he said that the Messenger of Allah used to struggle very hard to grasp the revelation and he used to move his lips (rapidly with the recitation). The narrator, Sa`id, then said, "Ibn `Abbas said to me, `I will move my lips like the Messenger of Allah used to move his lips (in order to show you).''' Then, the subnarrator said, "And Sa`id said to me, `I will move my lips like I saw Ibn `Abbas moving his lips (in order to show you).''' Then Allah revealed,

[لاَ تُحَرِّكْ بِهِ لِسَانَكَ لِتَعْجَلَ بِهِ - إِنَّ عَلَيْنَا جَمْعَهُ وَقُرْءَانَهُ ]

(Move not your tongue concerning to make haste therewith. It is for Us to collect it and that it be recited.) Ibn `Abbas said, "This means He will collect it in his chest to recite it.

[فَإِذَا قَرَأْنَـهُ فَاتَّبِعْ قُرْءَانَهُ ]

(And when We have recited it to you, then follow its recitation.) meaning, listen to it and pay attention.

[ثُمَّ إِنَّ عَلَيْنَا بَيَانَهُ ]

(Then it is for Us to make it clear (to you).) So after this, when Jibril would leave, he would recite it as Jibril had taught him to recite it.'' This has also been recorded by Al-Bukhari and Muslim. Al-Bukhari's wording says, "So whenever Jibril would come to him he would be silent, and when Jibril had left he would recite it just as Allah, the Mighty and Sublime had promised him.''