Socrates asks himself before the jury why he should have been so willing to pursue his line of philosophical inquiry if the resentment it has earned him has put his life in danger. He answers his own question, saying that when performing an action, the only relevant question to concern oneself with is whether one is acting justly or not. Considerations of life and death are selfish and unimportant next to considerations of justice. Since his calling to the philosophical life came from no lesser power than Apollo himself, Socrates should be even less willing to abandon his post as a seeker of truth than a good soldier would be to abandon his post in battle.
Socrates' wisdom comes from acknowledging that he does not know what he does not know, and his acknowledgment that he does not know what awaits him in the afterlife leads him not to fear it. A fear of death, then, is just another kind of false wisdom, of claiming to know the unknowable. On the other hand, he knows for certain that it would be wrong to disobey the will of Apollo and stop philosophizing, so he would be foolish to do what he knows is wrong for fear of an unknown quantity. Socrates goes further to suggest that if the court were to acquit him only on the condition that he give up philosophizing, he would refuse their offer, choosing to die rather than to abandon his duty to Apollo. His priorities are clear: wealth and honor are trifling concerns next to the pursuit of truth and the perfecting of the soul. This is the message he preaches to the youth of Athens, and unless such preaching corrupts them, he is innocent of the charges laid against him.
Putting an innocent man to death is far worse, and thus far more to be feared, than dying oneself, according to Socrates, and so really it is the jury, and not Socrates himself, that is in grave danger. In doing what he does, Socrates claims he is doing Athens a great favor, and he will not be easy to replace. In a famous passage, he likens himself to a gadfly and the state to a large, lazy thoroughbred horse. He is constantly buzzing about, waking his fellow citizens out of their sleep. Though his presence may be irritating, the state will be more awake and productive thanks to his services.
Unlike most Athenian men, Socrates has mostly kept aloof from politics and public affairs, preferring to interact with people on an individual level. He explains that this behavior results from a supernatural sign, an inner voice which comes to him and dissuades him from getting involved. This, he claims, is the only reason he has lived to the ripe old age of seventy, since no man who acts in opposition to the state, however justly, can survive for long. To prove his point, he refers to two occasions on which he opposed the authorities in the name of justice; in both cases, he nearly died from his bravery.
While in his more mature works, Plato asserts all sorts of positive doctrines (the most famous of which was his theory of forms), it is highly debatable whether Socrates advances any positive theses at all. On one hand, he quite explicitly claims that he knows nothing, and that his wisdom lies in his acknowledgment of that fact. On the other hand, there do seem to be some ethical principles that radically inform all of Socrates' thinking. For instance, he is famous for stressing the importance of knowing oneself and for asserting that no one ever knowingly and intentionally does evil rather than good.
In this section of the text, these ethical principles come into play in force as Socrates passionately defends the justice of the philosophical life. As he has already stated, his role as a philosopher is to question people regarding their own supposed knowledge and to show them that their wisdom extends only as far as their acceptance of their ignorance. In this respect, he is helping people gain wisdom (his kind of wisdom, that is) and overcome ignorance. Socrates implicitly associates wisdom with goodness and ignorance with evil, in accordance with his principle that no one knowingly does evil. If we are all uniquely wise, we cannot possibly do evil, since evil deeds are the result of ignorance above all else. Thus, leading the philosophical life is a supreme moral duty, as it is the most direct way of overcoming evil.