The miracle of the Mass
The priest, saying Mass with his back to the congregation, is performing a miracle at his altar, much like that of the alchemist, bringing God himself into presence in the bread and wine, out of the nowhere into the here: and it matters not, to either God, the priest, the bread, or the wine, whether any congregation is present or not. The miracle takes place, and that is what the Mass, the opus, the act, is all about.