This is a good question. There are several reason why Socrates is important. Let me offer a few of them.
First, Socrates is important, because he is one of the earliest philosophers in Western history. More importantly, he asked important question about life that still pertain to us.
Second, Socrates by his incessant questioning really makes people question what they know and how they know it. In other words, he makes people think about eternal things. For example, according to Plato's depiction of Socrates, Socrates believes in the eternal forms, which are unchangeable universals. So, when he talks about what is good, he is talking about the essence of goodness. In short, Socrates makes people think.
Finally, even if people do not agree with Socrates, he has put human inquiry on a new level.