[That is] so He may make what Satan throws in [i.e., asserts] a trial for those within whose hearts is disease1 and those hard of heart. And indeed, the wrongdoers are in extreme dissension.
The satan puts doubts in the recitation of the Prophet so that Allah makes what he puts as a test for the hypocrites and those idolaters whose hearts have become hard. The oppressors amongst the hypocrites and idolaters are in enmity of Allah and His Messenger, and distance from the truth and guidance.