A Robin Red breast in a Cage Puts all Heaven in a Rage. (5-6)
The Bat that flits at close of Eve Has left the Brain that won't believe. (25-26)
Our "Summary" pages cover the different animal metaphors and show how they unfold. So for the particular examples you should check them out. But, here, we just want to talk about animals in general, as symbols. What's the point of using so many animals in so many different ways? Blake seems to be saying that, if you can be sensitive to things that are happening in the animal world (a world that people typically consider to be less important than the human world), you can probably be sensitive to those same things when they happen in the human world. If a robin getting caged makes heaven angry, what about political prisoners? Isn't all tyranny and unjust imprisonment kind of awful?
At other times, Blake will use animals to symbolize things about human beings. For instance, the bat is an animal that symbolizes the thoughts of an unbeliever, in Blake's use of the image. Ultimately, these animals are our own powers and personalities—kind of like the way in Harry Potter, the "patronus" spell creates a protective animal spirit-thing that shows something about the person who casts the spell (that is, if you happen to know what we're talking about).