When Jesus talks about eternal life, he doesn't mean that we'll all be immortal (after all, there can be only one). He is referring to a spiritual life with God that continues even after death. Of course, in the Gospel of John, Jesus also shows death who's boss by raising Lazarus and then coming back from the dead himself. Now that's living on a prayer.
Questions About Life and Death
How is Jesus's resurrection different from Lazarus's? What purpose do the two scenes serve in the story?
How would the story be different if, instead of dying and being resurrected, Jesus was just immortal?
How is death portrayed in the Gospel of John? Is it always tragic and to be avoided?