WARNING: "stuff from a Time interview with GRRM" spoilers below
Poor Beric Dondarrion, who was set up as the foreshadowing of all this [resurrection], every time [he’s brought back] he’s a little less Beric. His memories are fading, he’s got all these scars, he’s becoming more and more physically hideous, because he’s not a living human being anymore. His heart isn’t beating, his blood isn’t flowing in his veins, he’s a wight, but a wight animated by fire instead of by ice, now we’re getting back to the whole fire and ice thing.
Poor Beric Dondarrion, who was set up as the foreshadowing of all this [resurrection], every time [he’s brought back] he’s a little less Beric. His memories are fading, he’s got all these scars, he’s becoming more and more physically hideous, because he’s not a living human being anymore. His heart isn’t beating, his blood isn’t flowing in his veins, he’s a wight, but a wight animated by fire instead of by ice, now we’re getting back to the whole fire and ice thing.
Maybe that's how.