I don't think it's a crack at religion. Schopenhauer lived in the 19th century, which was a time of intense, religious, philosophical enquiry. He saw the world as evil and full of suffering (which the realm of the Prince is, so no conflict with religion there), and he believed in salvation. The 'will' is opposed to 'perception', which agrees with the Christian view of God's will versus the worldly and sensuous. We are so worldly, and our perceptions are so flawed, so influenced by the realm of Satan, that we must work very hard to submit to the will of God. Free will? You bet! We are free to be evil -- it is the easiest thing, in fact... but we are also free to obey the will of God. The word 'will' is applied from two perspectives, our free will and God's divine will.