َ فَجَعَلَهُ غُثَاءً أَحْوَى ﴿۵﴾ سَنُقْرِئُكَ فَلَا تَنْسَى ﴿۶﴾ إِلَّا مَا شَاءَ اللَّهُ إِنَّهُ يَعْلَمُ الْجَهْرَ وَمَا يَخْفَى ﴿۷﴾

﴾5﴿ Faja'alahoo ghusaaa'an ahwaa
﴾6﴿ Sanuqri'uka falaa tansaaa
﴾7﴿ Illaa maa shaaa'al laah; innahoo ya'lamul jahra wa maa yakhfaa

﴾5﴿ Then He turned it into black, decayed straw
﴾6﴿ Surely, We will make you recite the Qur’an, so you will not forget
﴾7﴿ Except what Allah wills. Surely, He knows what is manifest and what is hidden

[6,7] At the beginning, there is good news, and in these two phrases are glad tidings: one is the completion of teaching the Qur’an, and the other is granting the power to preserve it: “We will make you recite” (سَنُقْرِئُكَ). This Surah is among the early Makki surahs, and in it, such a promise was made, which Allah the Exalted fulfilled with the completion of the Qur’an.
“So you will not forget” (فَلَا تَنْسَى) — this is a negation, conveying truthful information: that the Prophet (May Allah bless him and give him peace) would never forget the Qur’an — it remained preserved in his heart forever.
The second opinion is that this negation actually serves as a prohibition, and “forgetting” here means neglect or disregard — that is, do not neglect to recite and act upon it.
“Except what Allah wills” (إِلَّا مَا شَاءَ اللَّهُ) — according to the first meaning (negation), this refers to a form of abrogation known as "naskh by causing to forget (insā’)", as mentioned in Surah Al-Baqarah (2:106). Alternatively, the exception could be for blessing.
According to the second meaning (prohibition), the exception is disconnected — meaning: “Do not forget,” unless Allah wills for you to forget something through abrogation. (And this occurs by Allah's will), so it is not a sin.