Kundera always attacks his themes head-on. In this case, immortality is viewed from a few perspectives. On of those is historical: Kundera explores Goethe's struggle to remain the sole custodian of his own legend, thwarting his friend and literary rival Bettina's attempt to cut in on his action by writing his biography. Immortality here is a commodity, to be bought, sold, and when possible: stolen.
Kundera makes the point that the only immortals are artists and politicians. It's not clear in which category he places prophets.