!Fascist Russia is an easy way to get there. Russian Orthodox Christianity was so intensely tied to Russian Nationalism that they spent a large part of the nineteenth century converting Ukrainian Catholics at bayonet-point. Dostoevsky's rants about Poles and Jews also would not really be out-of-place in the mouth of Joseph Goebbels.
You would first need to create an Orthodox Theocratic revolutionary/reactionary movement in Russia. This is difficult, because the Russian Orthodox Church was firmly part of the Establishment that so badly failed in WWI. You would need a non-establishment Orthodox movement to form the nucleus of a theocratic movement, as local parish priests in Catholic countries were the nucleus of nationalist movements, and as the Church in Poland later served the anti-Communist movements. Maybe a particularly popular Orthodox mystic--importantly, one hostile to the Tsar. Maybe he comes to prominence in the Russo-Japanese War--some unit of the Russian Army has success against Japan, and he, a local monk/priest, is there with them, praying for them, preaching, giving him prominence. In his sermons, he blames the corruption of the established Church and Tsarist state for Russia's overall failure, and around him develops a sort of Taiping-ish movement to recreate Russia as a true Third Rome. None of this would be really alien to Russian tradition--maybe our cleric can be an Old Believer. Officially, they were outlawed until 1905--that could work either for or against them in this question.
Then you need a big national trauma to destroy the Russian establishment and allow these people to take power. Something like WWI. When the Tsarist government falls, our cleric plays Lenin and takes over. He has himself proclaimed Patriarch of Moscow and sets to work purifying Russia of heretical Catholic/Protestant influences. That means, of course, a purge of the Baltic Germans, the Ukrainian Catholics, and above all the Poles and Jews.
You would first need to create an Orthodox Theocratic revolutionary/reactionary movement in Russia. This is difficult, because the Russian Orthodox Church was firmly part of the Establishment that so badly failed in WWI. You would need a non-establishment Orthodox movement to form the nucleus of a theocratic movement, as local parish priests in Catholic countries were the nucleus of nationalist movements, and as the Church in Poland later served the anti-Communist movements. Maybe a particularly popular Orthodox mystic--importantly, one hostile to the Tsar. Maybe he comes to prominence in the Russo-Japanese War--some unit of the Russian Army has success against Japan, and he, a local monk/priest, is there with them, praying for them, preaching, giving him prominence. In his sermons, he blames the corruption of the established Church and Tsarist state for Russia's overall failure, and around him develops a sort of Taiping-ish movement to recreate Russia as a true Third Rome. None of this would be really alien to Russian tradition--maybe our cleric can be an Old Believer. Officially, they were outlawed until 1905--that could work either for or against them in this question.
Then you need a big national trauma to destroy the Russian establishment and allow these people to take power. Something like WWI. When the Tsarist government falls, our cleric plays Lenin and takes over. He has himself proclaimed Patriarch of Moscow and sets to work purifying Russia of heretical Catholic/Protestant influences. That means, of course, a purge of the Baltic Germans, the Ukrainian Catholics, and above all the Poles and Jews.