We (men) are animals, like the brutes, but we have a rational form, like the angels. Yet we are not angels trapped inside animal flesh, nor are we "spiritualized brutes."
We can understand the animal world, though not exhaustively. But how can we understand the angelic world? When most of us consider the angelic world, the resulting vision is a mish-mash of spiritualized non-sense. We have fond thoughts towards the angels, (they're cool right?) but we really don't have a grasp on what the angelic world is like.
Our attempt to understand the angelic world is something like a cow trying to understand the human world. A cow has frequent interactions with humans. The cow "sees" us... but not really. He sees an oddly shaped cow that makes strange noises I guess. He cannot comprehend our world. I think it must be something like that with the angels. We "see" them (that is, we see their effects) but we comprehend the angelic world about as well as a cow comprehends the human world.
A dog might live in New York City, surrounded by all the complexities of millions of rational beings doing things that are far too grand for the canine to grasp. But the height of his intellectual ambition is to find something to chew. Despite such proximity to the human world, he has no comprehension of what's happening all around him.
We are surrounded by an angelic world that is more complex that we can comprehend. And despite our proximity to such grandeur, the height of our intellectual ambition is to acquire the next thing that will bring us temporal pleasure.
Imagine if a dog was miraculously given the capacity to understand the human world. Imagine his reaction. I think if we were given the capacity to understand the angelic world - it would be something like that.