Midnight Mass Explained
6. Why Father Paul Can Walk In The Daylight
When Pruitt's vampiric secrets are unmasked midway through the season, viewers may be asking why a vampire has been able to spend a large part of the early episodes enjoying the quaint spring weather with his congregation. The sun proves to be a major problem for him later, so why is it not an issue when he arrives on the island?
The answer, it turns out, is a simple one which ties directly into the established vampire mythos. Put simply, Pruitt wasn't dead at this point. The vampire didn't kill him in Damascus, it gave him enough of its blood for Pruitt to heal and regain his youth, presumably so that he could transport the creature back to America with him.
Pruitt's death occurs when he collapses after having consumed too much of the vampire's blood, and it's the blood in his system which enables him to come back.
This is the same reason why the townsfolk don't transform into bloodsucking creatures until after they kill themselves in the penultimate episode, with only those "chosen" ones with enough of the blood in their veins coming back.