Both the Light and the Void essencially deals with both the matters of creating life and harboring the dead. Void are able to create life on worlds who are void of all light, were as creatures created by the light dies(or changes) where there is only void. Both of these cosmic forces also harbors the afterlife, in a myriad of different ways.
Being a priest devoted to the shadows means you must know the light, cause the brightest light casts the darkest shadows. As a shadow priest you walk dangerously close to the void, to hear it’s whispers, It’s truths and thus you also gain hints of what is to come both in this world and the next.
The voids visions show you not one truth but a myriad of truths, all this information might cause you to lose grip of what is perceived as the mortals reality. Mortals are commonly firm believers in the light, which usually have but one truth and shuns the others as lies.
As a shadow priest you don’t delve into undeath, cause undeath are unnatural and against the truths envisioned by the void. However you can be concerned about the spiritual side of the afterlife, thus the void teaches us that death is not the end but only the beginings of something far greater.
Thus being a shadow priest concerned with death, whould require you to have a firm belief that death is a means of freedom from the shackles that both life and undeath binds us with. You could basicly attempt to RP a member of the Cult of Forgotten shadows.