Why did Lily's enchantments work for Voldemort?

Question

Lily Potter chose to die instead of sacrificing her son Harry to Voldemort. In doing so, protective enchantments were created that protected Harry and made him less vulnerable to Voldemort and Voldemort's attempts to kill Harry.

Yet, I don't understand how Lily's enchantments, when Voldemort stole Harry's blood in the graveyard scene in Goblet of Fire (chapter 33, The Death Eaters), were helpful to Voldemort at all.

‘He took my blood,’ said Harry.

‘Precisely!’ said Dumbledore. ‘He took your blood and rebuilt his living body with it! Your blood in his veins, Harry, Lily’s protection inside both of you! He tethered you to life while he lives!’

_{Deathly Hallows - page 568 - Bloomsbury - chapter 35, Kings Cross}

Yet I wonder about the following canon information:

• Lily's enchantment was contingent upon Petunia Dursley giving Harry a home, which Petunia grudgingly did¹. It was the blood bond between Harry and Petunia, plus the fact that Petunia gave Harry a home, where he could return to once per year, that sealed Lily's protective enchantments and made them strong. Voldemort was never granted a home at the Dursleys, and in fact never stepped foot into the Dursleys' home at any point in canon.

• Never having been given a home at the Dursleys, how, then, did Lily, Petunia, and Harry's blood bond exist within Voldemort? Or did it? If it did, would it be because Harry and Voldemort were distantly related through the Peverell line?

• Lily's enchantments broke the moment Harry turned 17 and could not protect Harry any more². According to the Harry Potter Lexicon's page on Voldemort, Voldemort was 69 years old when he stole Harry's blood. If Lily's enchantment broke for Harry at age 17, why would the enchantments work for Voldemort when he was 69?

• Dumbledore tells Harry in Order of the Phoenix that Voldemort would not possess Harry because the love that fills Harry -- Lily's love -- is a force that Voldemort detests so greatly that he cannot bear to come into contact with it³. Yet the love Lily infused into Harry runs in his veins; Voldemort took Harry's blood, the blood that is imbued with Lily's love. How can he bear to be in contact with the love given to Harry in his own veins?

Given this canon information, why did Lily's enchantments work for Voldemort?

¹_{Half-Blood Prince - chapter 3, Will and Won't and Order of the Phoenix - chapter 37, The Lost Prophecy}
²_{Half-Blood Prince - chapter 3, Will and Won't}
³_{Order of the Phoenix - chapter 37, The Lost Prophecy}

Answer 1

I think you're confusing three separate, though closely related, phenomena.

The first is Lily's protection, which lived in Harry's blood. This is what made Harry's touch hurt Quirrell in book one. That, of course, is why Voldemort chose to take Harry's blood, and therefore part of the enchantment, into himself in book four: to make himself immune to it.

The second phenomenon, related but separate, is the protective charms on the Dursley house. These were something additional: they were placed there by Dumbledore. They were built on Lily's protective enchantment, but they were apart from it:

"[Petunia] may have taken you grudgingly ... yet still she took you, and in doing so, she sealed the charm I placed upon you. Your mother's sacrifice made the bond of blood the strongest shield I could give you."

"I still don't --"

"While you can still call home the place where your mother's blood dwells, there you cannot be touched or harmed by Voldemort. ... You need return there only once a year, but as long as you can still call it home, there he cannot hurt you. ..."

OotP, Chapter 37

Dumbledore specifically says that he placed the charm that protects the house. This, not Lily's original protection, is what broke when Harry turned seventeen or no longer called the house home; Dumbledore refers to that too in the quote above. (He actually only refers to the bit about Harry calling the house home, but I think it's clear from other places in the books that the "or Harry turns seventeen" is part of the same terms and conditions as "calls the house home".)

There's no indication that Lily's enchantment broke when Harry turned seventeen. Actually, it ceased to be directly relevant as soon as Voldemort returned. By taking Lily's protection into himself, Voldemort rendered it moot: he could hurt Harry now. (Of course, that same protective enchantment had some pretty important indirect effects, which we saw in Deathly Hallows.) But Dumbledore's protective enchantment on the house was still quite effective, even though Voldemort had Harry's blood.

The third phenomenon is love, which is what drove Voldemort out when he was possessing Harry. Not Lily's protective enchantment, or even Lily's love specifically; in fact, it happened to be Harry's love for Sirius:

Let the pain stop, thought Harry. Let him kill us... End it, Dumbledore... Death is nothing compared to this...

And I'll see Sirius again...

And as Harry's heart filled with emotion, the creature's coils loosened, the pain was gone, Harry was lying facedown on the floor...

The reason Voldemort could take Harry's blood into himself, without suffering the same pain as when he possessed Harry, is that they were separate phenomena. What Voldemort took into himself was the ancient enchantment that Lily evoked and that lived on in Harry's blood. What drove him out when he was possessing Harry was the experience of the emotion of love.

Answer 2

I'm adding this as an answer as there was not enough space in the comments.

"You all know that on the night I lost my powers and my body, I tried to kill him. His mother died in the attempt to save him - and unwittingly provided him with a protection I admit I had not foreseen.... I could not touch the boy. His mother left upon him the traces of her sacrifice... This is old magic, I should have remembered it, I was foolish to overlook it.... but no matter. I can touch him now.

.....

I wanted the blood of the one who stripped me of power thirteen years ago... for the lingering protection his mother once gave him would then reside in my veins too...

-- Harry Potter and the Goblet of Fire - Chapter Thirty Three: The Death Eaters

So, Voldemort took Harry's blood believing that the protection that Lily left for Harry would reside in his veins too -- he is satisfied that just by being able to touch Harry - he has gained the powers of his mother's protection.

"He said my blood would make him stronger than if he's used anybody else's" Harry told Dumbledore. "He said that the protection my- my mother left in me - he'd have it too. And he was right - he could touch me without hurting himself, he touched my face".

For a fleeting instant, Harry thought he saw a gleam of something like triumph in Dumbledore's eyes. But next second Harry was sure he had imagined it, for when Dumbledore had returned to his seat behind the desk, he looked as old and weary as Harry had ever seen him.

"Very well", he said, sitting down again. "Voldemort has overcome that particular barrier."

-- Harry Potter and the Goblet of Fire - Chapter Thirty Six - The Parting of the Ways.

That which Voldemort does not value, he takes no trouble to comprehend. Of house-elves and children’s tales, of love, loyalty, and innocence, Voldemort knows and understands nothing. Nothing. That they all have a power beyond his own, a power beyond the reach of any magic, is a truth he has never grasped. He took your blood believing it would strengthen him.

-- Harry Potter and the Deathly Hallows - King's Cross.

From both the quotes, Dumbledore makes it clear that Voldemort had misunderstood how the protection left by Lily works. Instead of making Voldemort stronger - the fact that Harry's blood runs in Voldemort actually made Harry stronger. Voldemort could not kill Harry as long as Harry's blood was running in his own body.

I believe that Lily's enchantments never worked for Voldemort - because they were never intended to. And this is evident from the fact that Voldemort did not survive in the end.

As for the questions asked:

1) Lily's enchantment contingent upon Harry living with Petunia Dursley - as others have pointed out, it wasn't Lily's enchantment but ones Dumbledore had placed upon the Dursley's when he trusted Harry to be with Lily's blood relatives.

2) The blood bond between Voldemort and Harry was limited to the fact that Voldemort rebuilt his body from Harry's blood. It only gave another living body to add to Harry's protection. Harry was tethered to life while Voldemort lives.

3) Again - from Harry Potter and the Half-Blood Prince, Chapter three - Will and Won't:

The magic I evoked fifteen years ago means that Harry has powerful protection while he can still call this house 'home'.

That shows that only Dumbledore's will break when Harry turned seventeen.

4) When Dumbledore speaks of love in the Order of Phoenix - I do not believe he was referring to Lily's love. I believe he was referring to Harry's ability to love. Harry's love for the people closest to him was so strong that he would do anything for the one's he loved - as is evident by his rush to save Sirius.

"There is a room in the Department of Mysteries," interrupted Dumbledore, "that is kept locked at all times. It contains a force that is at once more wonderful and more terrible than death, than human intelligence, than the forces of nature. It is also, perhaps, the most mysterious of the many subjects for study that reside here. It is the power held within that room that you possess in such quantities and which Voldemort has not at all. That power took you to save Sirius tonight. That power also saved you from possession by Voldemort, because he could not bear to reside in a body so full of the force he detests. In the end, it mattered not that you could not close your mind. It was your heart that saved you".

-- Harry Potter and the Order of the Phoenix - Chapter Thirty Seven - The Lost Prophecy

Also - going back to the first book:

"Your mother tried to save you. If there is one thing Voldemort cannot understand, it is love. He didn't realize that love as powerful as your mother's for you leaves its own mark. Not a scat, no visible sign... to have been loved so deeply, even though the person who loved us is gone, will give us some protection forever. It is in your very skin. Quirrell, full of hatred, greed and ambition, sharing his soul with Voldemort, could not touch you for this reason. It was agony to touch a person marked by something so good."

-- Harry Potter and the Sorcerer's Stone. Chapter Seventeen: The Man with the Two Faces.

It was Lily's love that resided in Harry's blood. And Voldemort seems to have overcome that problem by using the blood to regenerate his body - as Dumbledore noted. But it was Harry's love for others (Not Lily's love for Harry) that made it impossible for Voldemort to possess Harry.

Answer 3

Lily’s sacrifice was a positive force that gave him another chance.

There were many parts to Harry’s protection by love, only one of which worked for the Dark Lord. As for why any part of the sacrificial protection worked to temporarily save the Dark Lord, J.K. Rowling addresses this in an interview. Lily’s sacrifice was “a positive force, a few drops of goodness” and by using Harry’s blood, the Dark Lord got one last chance at redemption.

She explains on her website that this encounter involves some very deep laws of magic, which Voldemort himself did not understand: "Having taken Harry's blood into himself, Voldemort is keeping alive Lily's protective power over Harry — except that the power of Lily's sacrifice is a positive force that not only continues to tether Harry to life, but gives Voldemort himself one last chance ... Voldemort has unwittingly put a few drops of goodness back inside himself; if he had repented, he could have been healed more deeply than anyone would have supposed. But of course, he refused to feel remorse." Also, since Voldemort is using the Elder wand, which actually belongs to Harry, neither the Cruciatus or the killing curse work properly. "The Avada Kedavra curse, however, is so powerful that it does hurt Harry, and also succeeds in killing the part of him that is not truly him, in other words, the fragment of Voldemort's own soul that is still clinging to his. The curse also disables Harry severely enough that he could have succumbed to death if he had chosen that path."
_{^{Time interview (2007)}}

The protection on the Dursleys’ house was a separate enchantment. That one is the one that broke when Harry turned seventeen, meaning he’d no longer be ensured of protection within the Dursleys’ house.

The other protection that Lily gave him was not dependent on Petunia keeping him, nor was it tied to the Dursleys house - it protected Harry from the Dark Lord wherever he was, like at Hogwarts fighting Quirrell. In addition, it didn’t expire when he was seventeen. The Dark Lord took Harry’s blood to attempt to make himself immune to this protection when Harry was either fourteen or fifteen, so at least part of it became ineffective then, but not because it naturally expired.

What protected Harry from being possessed in the Ministry had nothing to do with Lily. The Dark Lord was successfully possessing him, able to stay in his body, until Harry thought of seeing Sirius again and filled himself with his own love.

Answer 4

My answer will be similar to @JoeWhites (Joe - if you feel it's a direct duplicate, please say so and I'll delete it).

You asked:

• Never having been given a home at the Dursleys, how, then, did Lily, Petunia, and Harry's blood bond exist within Voldemort? Or did it? If it did, would it be because Harry and Voldemort were distantly related through the Peverell line?

2 separate answers to that:

1. Harry's blood existed within Voldemort since he used Harry's blood to create his new body.

   "B-blood of the enemy…forcibly taken…you will…resurrect your foe."
   Harry could do nothing to prevent it, he was tied too tightly….Squinting down, struggling hopelessly at the ropes binding him, he saw the shining silver dagger shaking in Wormtail's remaining hand. He felt its point penetrate the crook of his right arm and blood seeping down the sleeve of his torn robes. Wormtail, still panting with pain, rumbled in his pocket for a glass vial and held it to Harry's cut, so that a dribble of blood fell into it.
   He staggered back to the cauldron with Harry's blood. He poured it inside. The liquid within turned, instantly, a blinding white.

2. Lily/Petunia's blood had nothing to do with it. It was Harry's blood that carried Lily's protection (as Joe White's answer eluded to), and it was against that protection (that Voldemort could not touch/harm Harry) that the using Harry's blood was inoculating Voldemort against.

   Note that Death Eaters/Voldemort STILL could not attack harry in Petunia's house even after Voldemort took his blood.

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• Lily's enchantments broke the moment Harry turned 17 and could not protect Harry any more. According to the Harry Potter Lexicon's page on Voldemort, Voldemort was 69 years old when he stole Harry's blood. If Lily's enchantment broke for Harry at age 17, why would the enchantments work for Voldemort when he was 69?

• The enchantment was on Harry's blood. It didn't matter where the blood was residing - it was the fact that Harry's blood was there (as your own quoted Dumbledore statement shows - Your blood in his veins!).

• As aside, what broke at 17 was NOT Lily's enchantment but Dumbledores, as Joe said - but for the purposes of answering this bullet point that is irrelevant.

  Even if Lily's enchantment would break, it would break when Harry - and Harry's blood - turned 17, not when some other vessel of that blood (Voldemort) did.

Answer 5

I'm not sure anyone has responded to this directly, but in my opinion, Privet Drive was only Harry's home because both Petunia and Harry knew he had no where else to go, until he was magically considered an adult. At that time Petunia would no longer feel an obligation to house him. As such, it is that age, 17, when the 'consider the place your mother's blood dwells home' would break, because he would no longer be required to remain there, he would be his own person, legally, and both he and Petunia would no longer have a reason for him to have to consider that place his home. And that is why Dumbledore's wards on the house fell on that day, as opposed to any other time.