وَمَثَلُ الَّذِينَ كَفَرُواْ كَمَثَلِ الَّذِي يَنْعِقُ بِمَا لاَ يَسْمَعُ إِلاَّ دُعَاء وَنِدَاء
...
And the example of those who disbelieve is as that of him who shouts to those (flock of sheep) that hear nothing but calls and cries.
Allah made a parable of the disbelievers, just as He said in another Ayah:
لِلَّذِينَ لاَ يُوْمِنُونَ بِالاٌّخِرَةِ مَثَلُ السَّوْءِ
For those who believe not in the Hereafter is an evil description. (16:60)
Similarly, Allah said here
وَمَثَلُ الَّذِينَ كَفَرُواْ
(And the example of those who disbelieve...),
meaning, in their injustice, misguidance and ignorance, they are just like wandering animals, not understanding what they are told; if the shepherd heralds them or calls them to what benefits them, they would not understand what is actually being said to them, for they only hear unintelligible sounds.
This is what is reported from Ibn Abbas, Abu Al-Aliyah, Mujahid, Ikrimah, Ata, Al-Hasan, Qatadah, Ata Al-Khurasani and Ar-Rabi bin Anas.
...
صُمٌّ بُكْمٌ عُمْيٌ
...
They are deaf, dumb, and blind.
means, they are deaf, as they do not hear the truth; mute, as they do not utter it; and blind, as they do not see or recognize its path and way.
...
فَهُمْ لاَ يَعْقِلُونَ
So they do not understand.
means, they do not comprehend or understand anything.