An interesting analogy for
life. The theory goes that there is nothing but
darkness outside until the
sparrow flies through an open window into a room. For one small and brilliant moment everything is bright and warm and joyful-- up until the sparrow flies out the other window and back out into the bleakness and mystery of
eternity.
Also used with some effect in Small Gods, by Terry Pratchett, to describe the nature and existence of Gods. They are small, insignificant creatures until bolstered by belief. With the belief they grow and are made powerful, and are truly 'within the room'. But when the belief fades all too soon, they fade away, to be left voices on the wind with memories of what once was and will probably never be again.