The mainstream of Christianity has never been all too mystical, except for maybe in the very earliest days. Nevertheless, there's always been a running undercurrent of Esoteric Christianity, in the form of the Rosicrucians, the Behmenists, and even people like Origen and Clement of Alexandria. How could said undercurrent have become the major 'strain', as it were, of Christianity, and what would the effects be? Maybe Origen and his teachings are not condemned, but embraced by Christianity? I'm not sure what the best point to start from would be here. I'm assuming very early, though.