Knowledge is mysterious.
Obviously, this book is about knowledge, since that is precisely the question that Socrates asks Theaetetus about. But that makes the book entirely ironic, because like Theaetetus explains in his first answer, knowledge comes in many ways and is useful for a variety of purposes in the human life. Although that felt sufficient, Socrates takes this moment to show Theaetetus that he has avoided the real issue: Why are humans experiencing knowledge in the first place? What is the nature of human thought?
Human death is the only true problem.
Another irony is the dramatic irony that Socrates knows that public opinion is swaying against him. We learn this in the ending when he departs to attend a court hearing, probably the one where he will be convicted and made to drink Hemlock, or perhaps that is still some time in the future, but there is simply no getting around it—Socrates knows that human death awaits him and each of his students, and Plato certainly knows it, since by the time the book was written, his teacher had died.
The universe is understandable.
The existence of human knowledge is predicated on another fact that humans take for granted, that the universe is orderly and discernible, which is a completely ironic facet of reality to take for granted, since it seems to be the most important feature of human reality. Not only is the universe the field of potential experiences, those experiences seem to be compatible with the human or animal experience in ways. When Socrates is discussing "Logos," it is this transcendental metaphysical order that he is referring to.
We don't really question our reality.
Ironically, it seems that the students are not really thinking through their experience's correctly. From Theaetetus, we see that the individuals are primarily interested in knowledge as a tool to improve one's life, but Socrates uses knowledge in the opposite way, removing assumptions and things taken for granted. The goal of Socrates's knowledge seems to be to accomplish true skepticism about reality, not to succeed in life.
We cannot attain enlightenment alone.
But another irony categorizes Socrates. Secretly the reason he talks is the same reason for Plato's writing—it helps to shape the ideas into their full form by sharing them with others. Socrates would not be Socrates is he didn't concern himself with teaching his students. It seems even the enlightened few are unable to attain enlightenment except through relationship.
