The Naming of Cats," at its most basic level, talks about how cats have three different names. However, at a deeper level, the poem talks about identity and how people present themselves in different ways to the general public, to their family and friends, and to their most private self when they are alone.
In the poem, the first name a cat possesses is an "everyday" name that any observer can use:
First of all, there's the name that the family use daily,
Such as Peter, Augustus, Alonzo or James,
Such as Victor or Jonathan, George or Bill Bailey--
All of them sensible everyday names.
While some of these everyday names might be "fancier ... some for the gentlemen, some for the dames," they are, nevertheless, "all of them sensible everyday names." This is the "self" we let everyone see - our most public self.
However, the poem's speaker says one name is not enough. Cats also need a name that is ...
... particular,
A name that's peculiar, and more dignified,
Else how can he keep up his tail perpendicular,
Or spread out his whiskers, or cherish his pride?
This is a more individual name, a name that "never belong(s) to more than one cat." It recognizes the uniqueness that is that cat. This is the self we let our friends and family see - one that reveals some of our own uniqueness - our personal traits, talents, desires, likes, and dislikes.
However, even that name does not represent the cat at its deepest essence. That name is known only by the cat:
The name that no human research can discover--
But THE CAT HIMSELF KNOWS, and will never confess.
This is the self we only let ourselves see, our truest self, with our hidden desires, fears, dreams, beliefs, doubts, and concerns.
As for style, the poem is written in anapest tetrameter, with the accent (primarily) on every THIRD syllable (as marked in bold below):
You may think at first I'm as mad as a hatter
When I tell you, a cat must have THREE DIFFERENT