According to our Vulcan sources, Sha Ka Ree is a legendary location in Vulcan mythology. It's a very special planet located at the center of the universe—the place "from which creation sprang."
As noted by the film, places like Sha Ka Ree are ever present in mythology. Christians have Eden. Klingons have Qui'Tu. Romulans have Vorta Vor. Despite his adherence to a specifically Vulcan brand of spirituality, Sybok notes that all of these belief systems refer to the same real place.
This isn't an entirely controversial idea. While they don't comment on the "reality" of belief systems, many mythologists have argued that all religions share certain base elements and structure their mythology in similar ways. Sybok is simply updating this idea for a hip alien audience.
Of course, the key distinction is that Sybok believes that Sha Ka Ree (and, consequently, all religion) is literally real. This is proven untrue by the end of the film, at least in this instance. But even so, the idea that religions have more common elements than disparate ones is worth studying outside of an intergalactically minded theological debate.