"The Priest and the Bandits" is usually the very first side-quest that player's will come across when exploring the Crash Site, which revolves around the feud between a pair of Thieves, and a Priest that has cursed them to roam the Earth forever. One of the thieves will beg for your assistance, and depending on your choices throughout the story, you can either side with the Thieves, the Priest, or possibly even both. This is one of the few quests in the game where you will not gain any reputation.
In a cave by the Crash Site, you will discover the spirit of Charles Brehgo, a bandit. He will ask you to release him from his curse by killing the evil priest who cast it upon him. He will then mark Arbalah's House on your map.
Travel to Arbalah's House, and speak with the half-elfpriest inside. The priest will reveal himself to be Arbalah, and will explain to you that Brehgo and Fahrkus tricked him into letting them into his home, and attacked him and murdered his family. In anger and grief from the loss of his family, he placed a curse on them. He will then ask you to retrieve a Sacred Artifact for him, which Fahrkus stole.
Return to Brehgo's spirit in the Crash Site Cave and demand that he tell you where Fahrkus is. The easiest method is tricking him into thinking Arbalah will release the curse if he helps you.
Travel back to the Crash Site Cave, and tell Brehgo that Arbalah is dead. After a brief conversation, he will dissapear and you will be left there, free to loot any items you wish from the cave (if you haven't already).