Religious practice has dramatically changed (more than once in opposite directions) in Russia during the last 150 years or so--and the theological basis for the revolutionary changes really goes back to the founding days of the Christian church. Maybe the earliest documented split goes back to the Gospel of Thomas and early gnosticism, but the linked book chapter gives a helpful historical account from a Russian perspective. It's really only quite recently that the visibility of Christian practice has been completely restored in Russia. I attended a Russian Orthodox service at Tolstoy Farm in New York in the early 70's when the onsite monastery was the only one left in the world.
Ten or fifteen years ago, some of my friends toured Russia and found many of the old churches nearly abandoned. A few years ago, what they observed was dramatically different--much like the scenes in the Youtube that I linked above.
I think the breaking point with atheism goes back to WWII, when Stalin first ruthlessly closed, then reopened the Orthodox churches--to combat the Nazi's, and allegedly finally finding his own way back to the church. In Russian folk music, this song is sometimes claimed to be a reflection of Stalin's life:
In any case, the communists continued to back off. When Billy Graham was allowed to carry out Christian evangelism in Russia, he was amazed to discover that more Russians were going to church in Russia than in the USA.
Interesting times in Russia right now.