How did Harry change after getting the stone from Voldemort?

Here's the quote for that and the real description:

I met him when I traveled around the world. A foolish young man I was then, full of ridiculous ideas about good and evil. Lord Voldemort showed me how wrong I was. There is no good and evil, there is only power, and those too weak to seek it...

Professor Quirrell, Page 291

This passage occurs when Harry comes face to face with Professor Quirrell (and Voldemort) in the dungeons of Hogwarts. Harry finally begins to understand Voldemort's power to corrupt and the fine line between good and evil in the wizarding world. Professor Quirrell began as a "good" wizard but, after meeting Voldemort in Albania, developed a skewed perception of morality based entirely on power and those who are strong enough to seize it. Even though he tries to kill Harry, Professor Quirrell is still a somewhat sympathetic character because of the extent of control that Voldemort has over him. Quirrell's obedience to Voldemort is based on fear and personal weakness rather than loyalty or love: Rowling suggests that resisting Voldemort and his seductive power requires far more personal strength than many wizards possess.