This is reminding me of Vonnegut's Trafalmadorian retelling of the Christ story. The Trafalmadorians tell it something like this: There was this guy named Christ that went around telling everyone that he was the Son of God. Everyone thought he was crazy and an asshole, and eventually he got on everyone's nerves so much that they crucified him to get him to shut up.

Whereupon God appeared and said, "Well, he wasn't my son, but I'm adopting him now, so he is."

So, the moral becomes not that the sacrifice worked because he was born the Son of God. In fact, it wasn't so much of a sacrifice as someone annoying people to the point where they decided to kill him. The moral is similar to Ratatouile. Not that everyone can be a great cook, but that a great cook can come from anywhere.

Anyone could be the Son of God. Even if they're just a crazy jerk who won't shut up. Even if there was nothing remotely special about the way they were born. Because what's to stop God from adopting you at the last moment?

****

But getting back to Harry. What's disappointing with Peter (and a lot of the other magic spells in the series) is that while the magic is built up as metaphorical, it turns out to be a lot more prosaic. That life debt didn't fulfill itself in a deep and mystical way. It was just... plain old magic.