At the age of one, Harry Potter survived the killing curse, a curse which we later learn is unblockable, and vanquished Voldemort in the process. How he survived was unknown for ten years, but at the end of his first year at Hogwarts, he was told by Dumbledore that what saved him was his mother, Lily, sacrificing her life to save his.
But how much do we actually know about this protection? We are told a little explicitly in the series:
- It caused Voldemort's curse to rebound, killing Voldemort instead of Harry
- Quirrel, possessed by Voldemort couldn't touch Harry, and in fact touching Harry killed him
- Voldemort couldn't possess Harry without risking his own destruction
However if we read between the lines, we find quite a number of cases where Harry was protected from harmful spells hidden throughout the series.
You might ask how Harry could be affected by (insert appropriate harmful spell here)? The answer, in my opinion, is that Harry's protection is from spells that, when finished, leave injuries or damage that can or can't be reversed using magic but never heal on their own.
Harry Potter and the Sorcerer's Stone
Obviously, the place to start is the curse that didn't kill Harry. The Avada Kedavra curse, as we learn in Goblet of Fire, is unblockable, leaves no marks on the victim, and causes no damage except killing the target. And yet, when Harry's protection came into play, the spell was blocked, left a mark on baby Harry's forehead, and blew up the part of the house he used it in.
However, this protection is more than just a one time event, or even just protection from one particular curse. My theory, based on the evidence produced here, is that it protects Harry from other spell damage, or in one case, damage done by a spell being lifted. It does this through active protection such as we already were informed of, and by passive protection, working in similar ways to Felix Felicis to make events conspire for Harry's continued survival.
One example of passive protection is found at the end of the book when Harry is trying to protect the stone from Quirrel, and as Dumbledore says later "The effort nearly killed you, Harry". It seems to me that Dumbledore arrived just in time because of the protection of Lily Potter's sacrifice.
In fact you might even go so far as saying (and I certainly do) that the protection was responsible for Firenze, the one centaur who didn't consider it beneath his dignity to give Harry a ride to safety on his back, being near the dead unicorn rather than wherever the rest of the herd was. It's also responsible for the fact that when Hermione went to stop Snape, thinking he was jinxing Harry's broom, she accidentally knocked Quirrel over.
Harry Potter and the Chamber of Secrets
While being taken from his house to be sent to Azkaban, Hagrid said that if anyone wanted answers, they should follow the spiders. Harry and Ron take that advice and find the spiders swarming into the Forbidden Forest. In the forest they come across a Ford Anglia they knew from earlier, and got snatched from behind by an Acromantula (see Fantastic Beasts) which carried them a long way, to a large colony headed by Aragog, Hagrid's old pet. Just before they get eaten they are saved by the Ford Anglia. Now we need to understand how the car got there:
- Dobby tried to prevent Harry from getting onto the Hogwarts Express
- Ron was with Harry
- Ron suggested taking the car
- The car crashed into the Whomping Willow
- And ran off into the forest
- Only then could it happen to drive into the colony
Seems to me that at least some of these are affected by Harry's protection to ensure that he would survive.
Later in the Chamber of Secrets, Gilderoy Lockhart tries to use a Memory Charm on Harry and Ron and, (compare with the Avada Kedavra) it rebounded on the wizard who cast it, and caused the tunnel to collapse. (It also destroyed Ron's wand but that might be the damage to the wand)
Harry Potter and the Prisoner of Azkaban
A mere five hours after Harry's feeble attempts at a Patronus Charm failed against “at least a hundred” dementors, he managed to arrive just in time to drive them off with a true patronus. The only previous time he managed a corporeal patronus was against Malfoy, Crabbe and Goyle, not even against a single “dementor” played by a boggart. In addition, it's a spell which is so advanced even Hermione had trouble learning it two years later in DA meetings. It also required a chain of prerequisite events:
