Though it seems like a mistake in Netflix's Midnight Mass, there's a reason why Father Paul could walk in the sun and Riley couldn't. Created by Mike Flanagan, Midnight Mass tells the story of new arrivals shaking up life for a sleepy, isolated community on Crockett Island. In the series, a disgraced former resident, Riley Flynn (Zach Gilford), returns home, trying to live with his tragic past mistakes. At the same time, a mysterious young priest named Father Paul (Hamish Linklater) also arrives, bringing miracles and renewing the community's vigor for religion. But things aren't as they seem, and the miracles come at a cost.
Midnight Mass eventually reveals that Father Paul has a dark secret. The character is actually Monsignor Pruitt, Crockett Island's former spiritual leader. Pruitt had dementia and became lost on a trip to Jerusalem, eventually ending up in a cave. There, he encountered a vampire, which pinned him down and fed on his blood. However, ignoring all the clear signs that it was a vampire, Pruitt believed the Midnight Mass creature was an angel. The encounter restored Pruitt's youth, so he took on the alias of Father Paul and brought the monster back with him to Crockett Island to give everyone eternal life.
In episode 4, Midnight Mass seemingly introduces a plot hole with Father Paul. During the episode, Riley goes to see Father Paul late at night, and he encounters Paul and the vampire. The vampire immediately springs on Riley, killing him and drinking his blood. Riley later awakes as a vampire, thirsting for blood and burning up in the sunlight. However, there's also a problem. After the vampire attacked Monsignor Pruitt/Father Paul, he could still walk in the sun for a while. So why couldn't Riley? The Midnight Mass question has confused fans, but there's a simple explanation.
The vampire killed Riley, but it didn't kill Monsignor Pruitt. Though it appears that Pruitt/Paul died during his encounter with the vampire in the cave, that isn't the case. The vampire even offered him some of its own blood to nurse him back to health. Pruitt actually died on the floor in the clergy house near the church in episode 3. He even clarifies this to Riley in episode 5, saying, "I died on the floor, just across the way there." Following Pruitt's death, he becomes a full vampire, developing his aversion to the sun and his hunger for blood. On the other hand, Riley died immediately. Paul/Pruitt even had to straighten out his broken neck when he woke up. Because of that, Riley instantly took on vampiric qualities.
The confusion all stems from Pruitt's inexplicable death. Before episode 3, Pruitt was still alive and could walk in the sun. However, his death changes things, making him a full vampire. The cause of Pruitt's death is a mystery. While it could've had something to do with his vampire encounter taking a toll on him, Bev (Samantha Sloyan) is a possible culprit. After all, Pruitt ultimately dies coughing up blood like Joe Collie's (Robert Longstreet) dog, and Midnight Mass heavily implies that Bev killed the dog with rat poison. Pruitt's death is still confusing, but it's not a plot hole.