He is not portrayed as rising again (actually, the description in the plot summary on wiki is him descending from heaven but I don't actually recall that), he is being used as a narrative voice. He does not interact with other characters or the scene, he simply sings a song that raises questions about just why Jesus did things the way he did. He is addressing the audience as much as anything.
Not everything in a movie, play, or novel really "happens", some of it is ways to comment on the action. Again, turn off your literal brain and try to understand what a "literary device" is. And if you can't grok that, then you're right. This play, and a lot of modern and postmodern literature and drama, is not for you.