The reason we cannot know.

Perhaps, to natures not wholly bad, sin is a poison of which the moral organization can only bear a certain fixed amount, great or small, before rejecting it altogether and with loathing.

We do not know.

We speak of the workings of conscience, not understanding what we mean.

It is like that subtle something which we call electricity; we can play with it, command it, lead it, neutralise it and die of it, make light and heat with it, or language and sound, kill with it and cure with it, while absolutely ignorant of its nature.