Young Russians in search of faith are turning to Islam. But Sarachev’s forebears didn’t practice Islam the way he understands it today. Over a millennium, Tatars had developed a rich and complicated theology, comfortable with rational thought and mindful of the need to coexist with the Christian Russians. In Kazan, Tatarstan’s capital, the religious establishment endeavors to carry on that tradition today. But Soviet hostility to religion left most Tatars with only a perfunctory sense of their own Muslim inheritance. Growing up, Sarachev remembers, religion meant grandparents and holidays, and little else. Yet even then, just after the collapse of…