"He was more afraid than you were tonight Harry..." Dumbledore continued "You had accepted, even embraced, the possibility of death, something Lord Voldemort has never been able to do... So tonight when chose not to fight, Voldemort’s magic that flowed through the wand of Lucius Malfoy recognised you as it’s own kin. It was imbued with the same protection of familial magic that Lilly gave you when she sacrificed herself. The spell that hit could not pass through those defences as it was now infused with them..."