Another one of Tarkovsky's subtle but strong exposure of the bloody past of Christianity in an era (1408) when Christians were the prosecutors. Russia had millennia old tradition of paganism (like the rest of Europe), which survived until the Stalin years. The witch-hunting started with Emperor Theodosius of Byzantium in 390 AD, and lasted until the Renaissance, resulting in the complete extermination (or genocide) of anyone 'heretic', anyone having a belief different than whatever the Church dogma was at the time.
With beautiful hypnotic shots, Tarkovsky manages to take us back in time, to relive the Dark Ages in the Russian countryside, and to appreciate what was lost forever, as he does in the rest of the movie.
The scene depicted here is a pagan ritual called Kupala Night, or Witche's Sabbath as Rublev describes it, a celebration of the summer, the sun, and fertility, which Orthodox Christianity stole and called it St. John's Day, June 24, it's the one people jump over fires.. or at least they used to, until recent years.
Andrei Rublev from curiosity sneaks into the festivities, but gets caught and his life is in danger, being a monk among pagans.. he ends up being tied up on a cross, to mock Jesus.. one of the pagans, a simple girl, would teach him that Love is unconditional, and will eventually free him and save his life.. the next day, her life is in danger, being hunted by the Christians, but Andrei - like another Peter - would just look the other way instead of helping her ...