Trying to identify a short story: The last man on Earth is walking across a shattered wasteland. After a time he's joined by someone he's never met before, but our original person is still the last man on Earth, because the new companion is rather different, probably not a man.
Every hour or two a voice booms out of the sky saying something like, "Bow down before me!", or "I am the Alpha and the Omega!"... things of that nature. The companion is friendly, sensible and helps the man, who begins climbing to the top of a nearby mountain. After climbing for a while the loud voice booms out again, saying something like, "Worship me!" The man finally turns to his unusual companion and asks, "Was he always insane?" and the companion sadly nods his head and mournfully says, "Yes, he's always been insane." We realize the booming voice comes from God and the kind companion is the Devil. ......Does anyone know the title or author, please?