There are many the quests in Warcraft that I always like to do either for reward reasons or for lore reasons. Two of my favorites, The Hero of the Mag'har chain and The Battle for Undercity, not only are amazing lore stories but also manage to get Thrall to leave his throne.
One quest that I always like to do when I have time is the Tale of Valor quest chain from Tirion Fordring in Crusaders Pinnacle. Tirion asks you to find Crusader Bridenbrad who he fears has succumbed to the Lich King's plague. Traveling to the snowy peaks of Icecrown you find Bridenbrad barely alive and, as Tirion suspects, infected with the plague. Tirion is determined to save him and sends you all over Azeroth and Outland to ask for help: Keeper Romulus, Alexstraza and A'dal. All offer their most powerful spells for our dying paladin but none can fully cleanse him of the blight. As death is inevitable, A'dal appears by our hero's side. He promises him a peaceful death and as he ascends to the sky A'dal assures you that the crusader "shall only taste paradise".
After all the non-stop violence, death, bloodshed and gore it is very refreshing and comforting to truly save someone. In a land where death can mean undeath seeing him lifted up into the heavens always makes me happy.
Take whatever religious meaning you like from the Narru's - their blinding white light, telepathy and calming music that fills you when they are near. They represent one of the higher beings in WoW and,I find it reassuring to remember they are around.