Perhaps at root it can be said that Faulkner is a significant writer in the US tradition of Modernist literature, the movement which from the late 19th century thru the 1940s considered ways to reflect things like the splintering of consensus in western societies, the effect of mechanisation and mass media, the discovery of the subconscious and the infinite variety of our internal mental lives by experimenting with new ways of story telling. Multiple points of view, non-linear narratives, unreliable narration, experiments with form and language, with grammar, punctuation, type etc etc were used by poets and novelists in various ways. Faulkner has received a lot of (valid) criticism recently for some of his views and his novels might seem dated, but at the last they are still part of the Modernist project and given a place among 'classics' for that reason. Doesn’t mean anyone has to actually like them of course (or even read them) but, if only for reasons of literary history, they are important.