What is the theme in A Ring of Endless Light by Madeleine L'Engle?

Death is the most predominant theme in this novel. Vicky and her family come to the island during the summer, planning to spend as much time as it takes to stay with Grandfather until he dies from the leukemia that is taking over his body. At the very beginning of chapter one, the family is attending the funeral of a friend who died trying to save someone else's life. Vicky has to come to terms with the impending death of her grandfather as well as the sudden death of her friend. While she is battling this, she finds out that one of the young men who is interested in her is actually suicidal. Not only that, but he is part of the group that calls themselves the Immortalists. They believe strongly in cryogenics. In fact, his own mother had died in a car accident the previous year, and the family had her body frozen.