Morrie refered to himself as a bridge, a person who is in between life and death, which makes him useful to others as a tool to understand both.

Wow, reflecting on this question, I can only come of with famous people who have died for a cause. In life they meant something great and in death, their message took on even greater significance hence the bridge. Consider Mahatma Gandhi who often spoke of dying before his time because of what he stood for. Also Nelson Mandela bridges this gap. Consider that when he is sick or on the verge of death, South Africa does a lot of soul searching.