I read this for a lit class. Here’s my interpretation:

Skellig was a guardian angel transformed to an angel of death. (I say “an angel of death” rather than “The Angel of Death” because how else would Skellig have so much time to lay sick, with all the death in the world, unless he was one of many?) He was weak because he had just taken the soul of his charge, Ernie Myers, the previous owner of the Falconer Road house. Skellig used to be Ernie Myers’ guardian angel. He used to watch him through the windows, listen to him, and eat his left over Chinese food and ale. When Myers’ time came, it was Skelligs duty to deliver him to heaven. But the process was comparable to what happens when a bee stings. The bee dies. So Skellig was naturally supposed to die after carrying out his duty (I know angels can’t die, but maybe he would be recycled, or something). But right before he died (Skellig became weak again prior to his last disappearance, “But worn out now,” he said, “Exhausted.”) Michael and Mina nursed him, giving him the chance to touch their lives, and the life of the baby. Thereby, Skellig experienced (temporary)strength and joy. Consequently, the triumphant baby was named Joy.