Por que Snape estava ajudando Harry o tempo todo?
Dumbledore responde isso:
"And there is something else..."
"Fire away."
"Quirrell and Snape-"
"Professor Snape, Harry."
"Yes, him - Quirrell said he hates me because he hated my father. Is that true?"
"Well, they did rather detest each other. Not unlike yourself and Mr. Malfoy. And then, your father did something Snape could never forgive."
"What?"
"He saved his life."
"What?"
"Yes..." Said Dumbledore dreamily. "Funny, the way people's minds work, isn't it? Professor Snape couldn't bear being in your father's debt... I do believe he worked so hard to protect you this year because he felt that would make him and your father even. Then he could go back to hating your father's memory in peace..."
Por que ele estava questionando Quirrell de que lado ele realmente estava?
Como mostrado em Dealthy Hallows (O capítulo do conto do príncipe), Snape estava apaixonado pela mãe de Harry, Lily. Quando ele se tornou um Comensal da Morte e ouviu parte da profecia, ele correu para contar a Voldemort sobre isso. Mas então ele percebeu que a profecia era provavelmente sobre o filho de Lily, e percebeu que Voldemort provavelmente iria matá-la. Depois disso, ele encontra Dumbledore para implorar-lhe para salvá-la:
"Hide them all, then," he croaked. "Keep her - them - safe. Please."
"And what will you give me in return, Severus?"
"In - in return? Snape gaped at Dumbledore, and Harry expected him to
protest, but after a long moment he said, "Anything."
A partir desse momento, Snape foi fiel a Dumbledore, e não a Voldemort.