We have not sent down the Qur'an unto you to cause you distress,
Juwaybir reported that Ad-Dahhak said,
"When Allah sent the Qur'an down to His Messenger, he and his Companions adhered to it. Thus, the idolators of the Quraysh said, `This Qur'an was only revealed to Muhammad to cause him distress.'
Therefore, Allah revealed,
طه
مَا أَنزَلْنَا عَلَيْكَ الْقُرْانَ لِتَشْقَى
إِلاَّ تَذْكِرَةً لِّمَن يَخْشَى
Ta Ha. We have not sent down the Qur'an unto you to cause you distress, but only as a Reminder to those who fear (Allah).
The matter is not like the people of falsehood claim. Rather, whomever Allah gives knowledge to, it is because Allah wants him to have an abundance of good. This like what is confirmed in the Two Sahihs on the authority of Ibn Mas`ud, who said that the Messenger of Allah said,
مَنْ يُرِدِ اللهُ بِهِ خَيْرًا يُفَقِّهْهُ فِي الدِّين
Whomever Allah wants good for, then He gives him the understanding of the religion.
Mujahid commented on Allah's statement,
مَا أَنزَلْنَا عَلَيْكَ الْقُرْانَ لِتَشْقَى
(We have not sent down the Qur'an unto you to cause you distress), "This is like His statement,
مَا تَيَسَّرَ مِنْهُ وَأَقِيمُواْ
So recite as much of the Qur'an as may be easy (for you). (73;20)
For, the people used to hang ropes at their chests (to hang on to when tired) in the prayer."
Qatadah said,
مَا أَنزَلْنَا عَلَيْكَ الْقُرْانَ لِتَشْقَى
(We have not sent down the Qur'an unto you to cause you distress),
"No, by Allah, He did not make it a thing of distress. Rather, He made it a mercy, a light and a guide to Paradise."
Allah said,
إِلاَّ تَذْكِرَةً لِّمَن يَخْشَى