170. " and when they are told: ` follow what allah has sent down,'
they say: ` nay! we follow what we found our fathers upon,'
even though their fathers had no understanding of anything nor
 were they guided aright."
171. " and the parable of those who reject faith is as the likeness 
of the one who shouts to that which hears no more than a call 
and a cry; deaf, dumb, and blind (are they) wherefore they
 do not understand.

commentary:

blind following of the ancestors is condemned
the previous verse warned us to avoid following the whispers and
footsteps of satan. now, in this verse, one of the examples of those
footsteps, which is the blind following of others, is pointed out. it says:

" and when they are told:
` follow what allah has sent down,'
they say: ` nay! we follow what we found our fathers upon,'..."

they mean that they do not care what the verses of allah say or
the messenger of allah invites to. so, in answer to them, the qur'an
says:

...even though their fathers had no understanding of anything nor were
they guided aright."

this statement refers to the fact that: if their fathers had no
wisdom and understanding by themselves nor had they accepted the
godly guidance of the prophets, then, would they follow their fathers
yet? if their ancestors or the infidels themselves had wisdom or were
guided, it would not matter, but it is not so.

there are two comparisons in this verse: 1) the likening of the
caller of truth to a shepherd; 2) the likening of infidels to some beasts
that understand nothing from the speech of the shepherd save a call and
a cry. this simile has been confirmed in a tradition by imam baqir
(a.s.), too. the parable means that the invitation of the prophet
(p.b.u.h.) from that faithless crowd to truth and breaking the dam-like
barrier of blindly imitation, is similar to the person who shouts to a
cattle of sheep or some animals in order to save them from danger but
they do not understand this message.

" and the parable of those who reject faith is as the likeness of
the one who shouts to that which hears no more than
a call and a cry; ..."

then, at the end of the verse, to emphasize more and to explain it
more clearly, it adds:

"... deaf, dumb, and blind (are they) wherefore they do not understand."