As novelist and critic A.N. Wilson says, "[Fyodor Dostoevsky's] views on religion are notoriously hard to pin down with confidence" (source). Hearing this is bit of a relief, isn't it? Some version of Russian Orthodoxy is practiced by many of the characters we meet in Crime and Punishment, and like many novels and films in the Gothic tradition (think The Exorcist), Christian imagery, ideas, and symbols are deployed for variety of purposes, some of them scary. All in all, religion and religious ideas are often contradictory and paradoxical in Crime and Punishment. We think that's part of the point Dostoevsky is trying to make – religion is an elusive force, which means something different to everybody.
By not pressuring Raskolnikov to share her religious beliefs when he's in prison, Sonia acknowledges that religion is a personal choice.