If once we admit, be it for a single hour or in a single instance, that there can be anything more important than compassion for a fellow human being, then there is no crime against man that we cannot commit with an easy conscience.
If goodness has causes, it is not goodness; if it has effects, a reward, it is not goodness either. So goodness is outside the chain of cause and effect.
As we live through thousands of dreams in our present life, so is our present life only one of many thousands of such lives which we enter from the other more real life and then return after death. Our life is but one of the dreams of that more real life, and so it is endlessly, until the very last one, the very real the life of God.
It may be suggested by some books that it is not a sin to kill an animal, but it is written in our own hearts - more clearly than in any book - that we should take pity on animals in the same way as we do on humans.