Professor Dumbledore is the Headmaster of Hogwarts School of Witchcraft and Wizardry. He has a great gift for inspiring loyalty: both Hagrid and Harry express their opinions that he's the best thing to happen to Hogwarts since sliced bread. In fact, Harry's faith in Professor Dumbledore is so strong that it brings Professor Dumbledore's phoenix, Fawkes, to rescue Harry from the basilisk's fang in the nick of time. In Book 2 at least, Harry believes absolutely that Professor Dumbledore is "the greatest wizard in the world" (17.76).
Professor Dumbledore is certainly a force for good. Still, there is evidence that he knows more about what is happening at Hogwarts than he is telling. After Colin Creevey is found Petrified outside the Hospital Wing, Professor Dumbledore comments, "The question is not who […] The question is, how…" (10.178). Why doesn't Professor Dumbledore just tell everyone – or even just Professor McGonagall – who the culprit is, if he knows?
This moment with Professor Dumbledore in Book 2 foreshadows the widening rift that's going to come between him and Harry over precisely this issue: why can he never just explain what's happening? For now, though, Harry is willing to put all of his trust in Professor Dumbledore without fully knowing why. Harry is still a child and not yet ready to be a leader, so he needs a figure of kindly authority to reassure him. It's not until Book 5 that he grows ready to move away from Professor Dumbledore's strong influence over him. It's not until Book 5, as well, that we begin to see Professor Dumbledore as a character with faults and flaws, instead of the benevolent, all-knowing power he appears to be in Chamber of Secrets.