why can gryffindor's sword destroy horcruxes?

Sword of Gryffindor Object information Manufacturer Ragnuk the First[1] Made Founder's Time (late 10th century)[2] Usage Muggle duelling[1]Slaying dark creatures[3][4]Destroying Horcruxes[3][4] Owners Ragnuk the First[1]Godric Gryffindor[1]Harry PotterAlbus DumbledoreSeverus SnapeRonald WeasleyUnidentified Snatcher (very briefly)GriphookNeville Longbottom [Source]

The Sword of Gryffindor was a thousand-year-old, goblin-made magical sword owned by the famed wizard Godric Gryffindor, one of the four founders of Hogwarts School of Witchcraft and Wizardry.[1]

The sword was later used in Albus Dumbledore's and Harry Potter's hunt for Horcruxes, as a tool of destruction against the Horcruxes, as means to destroy Lord Voldemort's immortality.

The Sword of Gryffindor was made in the 10th century by goblins, the magical world's most skilled metalworkers, and was therefore enchanted. Fashioned from pure silver, it was inset with rubies, the stone that represented Gryffindor in the hour-glasses that counted the House points at Hogwarts. Godric Gryffindor's name was engraved just beneath the hilt.[1]

The sword was made to Godric Gryffindor's specifications by Ragnuk the First, finest of the goblin silversmiths, and therefore King (in goblin culture, the ruler did not work less than the others, but more skillfully). When it was finished, Ragnuk coveted it so much that he pretended that Gryffindor had stolen it from him, and sent minions to steal it back.[1]

Gryffindor defended himself with his wand, but did not kill his attackers. Instead he sent them back to their king bewitched, to deliver the threat that if he ever tried to steal from Gryffindor again, Gryffindor would unsheathe the sword against them all. The goblin king took the threat seriously and left Gryffindor in possession of his rightful property, but remained resentful until he died.[1]

The story persisted, in some sections of the goblin community, that Gryffindor actually stole the sword from Ragnuk. This was a result of the cultural understanding of ownership that goblin-made items rightfully belonged to goblins, rather than the heirs of those who may have purchased them, a cultural understanding that should have been honoured by the wizards.[1][4]

During Hallowe'en of 1986, Slytherin student Merula Snyde decided to steal the Sword of Gryffindor from Godric's Hollow. After finding the crypt of Ragnuk in St Jerome's graveyard, the ghost of Ragnuk appeared, and when she revealed her intention to take the sword, he cursed her, completely blinding her, in response for her trying to take the sword. Jacob's sibling managed to convince Ragnuk to lift the curse from Merula and anyone else he cursed.[5]

In May of 1993, the sword materialised inside the old school Sorting Hat and appeared to Harry Potter, to whom the hat was given when he arrived in the Chamber of Secrets to save his best friend's sister, Ginny Weasley, from being drained of her life force by Tom Riddle's Diary and eaten by the Serpent of Slytherin. Harry used the sword to kill the Basilisk, which was hiding inside the bowels of the Chamber.[3]

This caused the sword to be imbued with basilisk venom (since goblin-made items only absorb what makes them stronger) and hence gained the ability to destroy Horcruxes, although Harry instead used one of the Basilisk's fangs to destroy the diary, which eliminated the sentient memory of Tom Riddle it contained and restored Ginny's vitality. After the events of that year, the sword resided in the Headmaster’s office and was kept safe within a glass case.[4]

During the summer of 1996, Albus Dumbledore used the sword on the Gaunt family ring. The sword cracked the stone in the ring, thus destroying it as a Horcrux. It still worked as the Resurrection Stone. Dumbledore tried to use it to talk to his deceased relatives, but failed.

Before he died, Dumbledore entrusted the sword to Harry in his will. However, Rufus Scrimgeour claimed that the sword was not Dumbledore's to give away. The Minister stated that it was a school heirloom, not personal property and refused to give it to Harry. This caused the trio substantial problems. Dumbledore placed an identical copy of the sword in his office, because he knew that the British Ministry of Magic would try to confiscate it and hid the real sword in a hole in the wall behind his portrait. Sure enough, the sword on display in the Headmaster's office was later taken by Rufus Scrimgeour for examination.[4]

When the sword was returned to the Headmaster's office by the Ministry, Dumbledore's Army students Ginny Weasley, Neville Longbottom, and Luna Lovegood attempted to steal it for Harry. The group was caught and punished as a result. Following that incident, Severus Snape passed the counterfeit sword to Bellatrix Lestrange. Bellatrix then stored it in her Gringotts vault alongside Helga Hufflepuff's cup, one of Voldemort's Horcruxes.

Upon discovering where Harry and his friends were camping out, Dumbledore's portrait instructed Snape to give Harry the real sword without Harry knowing that it was Snape, in case Voldemort found out through Legilimency on Harry. It also needed to be recovered "under conditions of need and valour". To fulfil these conditions, Snape deposited the real sword in a frozen lake in the Forest of Dean and used his corporeal Doe Patronus to guide Harry to the sword.

When Harry tried to retrieve the sword, the Locket of Slytherin closed around his neck and attempted to strangle him, sensing that its destruction was near. Ron Weasley came to Harry's rescue, retrieved the sword from the lake and used it to stab the locket, destroying it. Harry believed that Ron should be the one to perform the deed as he had recovered the sword, and Dumbledore had taught Harry about the power of certain acts.[4]

Later, Harry, Ron, and Hermione were captured by the Snatchers and the sword was taken by one of them as a spoil. They were then taken to Malfoy Manor where Bellatrix Lestrange noticed the sword. Though Bellatrix ordered the Snatcher to give her the sword, the man foolishly refused and was stunned along with his comrades.

Harry and Ron were then imprisoned in the cellar along with Luna Lovegood, Dean Thomas, Mr Ollivander and the goblin Griphook while Hermione was being tortured and interrogated by Bellatrix. Bellatrix demanded to know where the trio came into the possession of the sword, thinking that they had broke into her vault for it. She summoned Griphook to verify the sword, and at Harry's request, Griphook lied and said that it was a fake.[6]

When Harry and the rest were saved by Dobby to Shell Cottage, Harry asked for Griphook's assistance to break into Bellatrix Lestrange's vault at Gringotts, as he suspected the Cup of Hufflepuff - one of Voldemort's Horcruxes - was hidden within it. Griphook, impressed by Harry's respectful treatment of the house elf, agreed to help on the grounds that he would be given the real sword as payment. Harry agreed reluctantly.

When their break-in was discovered, Griphook seized the real sword and ran with it. Afterwards, the goblins were summoned to Malfoy Manor to deliver the news of the break-in to Voldemort; in a fit of blind rage, Voldemort murdered all those present for their failure in protecting the vault and one of his Horcruxes.[4]

In the Battle of Hogwarts, the sword reappeared in the Sorting Hat for Neville Longbottom and, while following Harry Potter's orders, he used it to behead Nagini, Voldemort's snake and his last remaining Horcrux with a single stroke of the blade, rendering Voldemort a mortal man once more.

The sword was last mentioned lying beside Neville in the Great Hall following the conclusion of the final battle and the end to the Second Wizarding War.[4]

During the mysterious Calamity which affected the wizarding world in the 2010s, the Sword of Gryffindor was one of the numerous magical items and artefacts that appeared scattered across the world, called Foundables for which volunteer wizards and witches of the Statute of Secrecy Task Force had to deal with in order to uphold the International Statute of Wizarding Secrecy.[7]

The Sword of Gryffindor was made of pure silver, and its hilt was set with egg-sized rubies — the gemstone that was used to symbolise the House of Gryffindor at Hogwarts. The full name of Godric Gryffindor was also engraved just beneath the hilt.

Much like a wand, the sword of Gryffindor appeared to be almost sentient, responding to appeals for help by Gryffindor's chosen successors. Whenever a "true Gryffindor" needed it, the sword would let itself be pulled out of another of Godric Gryffindor's artefacts — the Sorting Hat.[3][8] After Ron Weasley saved him from drowning, Harry believed that since it was Ron who recovered the sword it was Ron who had to use it because "Dumbledore had at least taught Harry something about certain kinds of magic, of the incalculable power of certain acts". In addition, the portrait of Dumbledore told Severus Snape that the sword must be taken under conditions of need and valour, which was why Snape put it into the frozen pond in the first place.[4]

Having been made out of goblin's silver, it only took substances which strengthened it into itself, which could then be used against enemies. Due to Harry Potter killing the Serpent of Slytherin with it, the sword was imbued with Basilisk venom and could destroy Horcruxes. This also means that it never rusted or required cleaning.[4]

The Sword of Godric Gryffindor is Goblin-made, and as such takes in the strengths of whatever it touches. Because of this, it can destroy horcruxes after taking in basilisk venom when Harry stabbed the Basilisk in The Chamber of Secrets .