"You did a very noble thing, in saving Pettigrew's life."
"But if he helps Voldemort back to power-!"
"Pettigrew owes his life to you. You have sent Voldemort a deputy who is in your debt. When one wizard saves another wizard's life, it creates a certain bond between them...and I'm much mistaken if Voldemort wants his servant in the debt of Harry Potter."
"I don't want a bond with Pettigrew!" said Harry. "He betrayed my parents!"
"This is magic at its deepest, its most impenetrable, Harry. But trust me...the time may come when you will be bery glad you saved Pettigrew's life."