I think this song is about protecting or watching over someone you care for. It seems like he is using the imagery of a night-light, evidently in the shape of a blue canary, to symbolize this. Maybe this is something he remembers from childhood. Many people have night-lights. And all he asks of the person that he watches over and cares for is that they make a little spot for him in their soul, that they hold him dear as he does them. Don't ask me about the verse with Jason and the Argonauts, but it does end with the same idea of a bluebird of friendliness, a guardian angel.