It's about a space colony, presumably centuries or millenia in the future. The world was not peopled by humans before the colonists' arrival, but there were native beings to be conquered.
Once those beings were conquered, the colonists and their descendants peopled the world. The colonists forced their descendants into a very rustic lifestyle, providing them immortality via reincarnation as their only "modern" convenience.
Presumably because of the reincarnation, the colonists styled themselves after (and were eventually accepted as) Hindu gods. I was very amused to run across the third picture in this collection a few minutes ago, showing one who featured prominently in the story.
The story starts, as I said, hundreds or thousands of years later. Two of the gods are reincarnating another (from the ether, rather than from another body), who was known variously as Kalkin, Gautama, Buddha, Maitreya (Lord of Light), and Mahasamatman. But he preferred to drop the maha- and -atman, and just go by Sam. As a resistance to the Hindu gods, he had resurrected Buddhism.
The story documents the struggle between him and the Hindu gods. Interestingly, though, after starting at the one point, it then drops back some length of time (probably 50-70 years, although it never actually says, so I'm guessing) and covers the build-up of how they got to that point. After spending most of the book on that build-up, the last couple of chapters document the final confrontation in the present.
I think I'm probably most amused by the extreme cynicism of the storyteller.
He never claimed to be a god, but then he never claimed not to be a god. Circumstances being what they were, neither admission could be of any benefit. Silence, however, could.
And yet, even in this cynicism, and even with admitting later that he had founded a religion he believed not a word of, he was still able to bring another to enlightenment. And I think that enlightened one did a great deal to rescue the cynicism.
And let's not ignore that it's a pretty compelling story, very well written.
It's Zelazny at his best, and that's saying quite a bit, in my mind.