This article is a roundup of six pieces written by literary critics, tasked with explaining what it is they do exactly, why they do it and why it matters. (Can anyone really answer that one? :))
I think the idea here is that today so many people have opinions about books expressed freely online (such as on this blog, for instance) that one wonders if professional literary critics are still relevant. I, for one, would say they are.
Professional critics have a depth of perspective and breadth of reading experience that gives them more than the average amount of insight when judging a literary work. But that's my .02.
If you'd like to read the six literary critics pontificate on the subject at greater length, check out the article and the links to the pieces within it.
But I suspect it pretty much boils down to what I just said in one sentence. :)