Didn't you know that Bulgakov was almost a Satanist? He had a priest for a father, whom he couldn't stand.

Bulgakov wasn't a Satanist, but an artist;)
"The Master and Margarita" is a work of fiction and nothing more (not a historical or religious treatise or anything of the sort). In any work of fiction, everything is subordinate to artistic imagery, rather than historical (or rather, pseudo-historical) authenticity.

Nevertheless, in terms of its religious message within an atheistic state, this novel can be considered an apology for Christianity (as a phenomenon as a whole). This is evidenced by many and many examples of atheists converting to Christianity during the Soviet era, specifically thanks to this novel.