Metaphor is probably not the best word but probably close.Could Christianity be a metaphor?
The essence of Christianity encapsulates many concepts and ideas that predated its inception. The reason it exists stems from two primary events. The first was the oppression of the Jews by the Romans and their desperate need to have a savior free them, and the decision by Constantine to have a new religion to replace the increasingly unpopular roman gods.
But throughout the creation process of this new religion there was always the archaic political perceptions and needs of authoritarianism, and reward and punishment. The myth makers knew these ideas well, they were ages old, and no one knew any better, and hence the Christ/Messiah/Savior character of Jesus evolved. It offered the ultimate in Utopian reward and punishment - believe in me and live for eternity or reject me and die. Note that the idea of hell was essentially a Christian concept, the OT does not reference a hell concept.
Once we cut through the 2 millenia of repeated myth, handed down throughout the generations, and realize that the savior concept is just that, a concept, then yes we could say that Christianity is a metaphor for an ages old authoritarian idea of ultimate reward and punishment.