In this quote, the Hatter emphasizes the importance of nuance and precision in language, showing how slight differences in phrasing can lead to very different meanings. He compares two similar statements to illustrate that although the words may seem alike, their implications are quite different depending on their arrangement.
The Hatter’s point is that phrases like "I see what I eat" and "I eat what I see" are not interchangeable because they convey different ideas, despite sounding similar. This highlights the whimsical and often paradoxical nature of language, a recurring theme throughout Lewis Carroll's works in exploring logic and meaning.