أَن جَاءَهُ الْأَعْمَىٰ
Because there came to him the blind man (i.e. 'Abdullah bin Umm-Maktum, who came to the Prophet (Peace be upon him) while he was preaching to one or some of the Quraish chiefs).
وَمَا يُدْرِيكَ لَعَلَّهُ يَزَّكَّىٰ
But what could tell you that per chance he might become pure (from sins)?
أَوْ يَذَّكَّرُ فَتَنفَعَهُ الذِّكْرَىٰ
Or that he might receive admonition, and that the admonition might profit him?
وَمَا عَلَيْكَ أَلَّا يَزَّكَّىٰ
What does it matter to you if he will not become pure (from disbelief, you are only a Messenger, your duty is to convey the Message of Allah).