" Dumbledore wanted the Elder Wand to recognize the mercy and regret in Snape’s Killing Curse and transfer allegiance to Snape, quietly. He knew he could trust Snape to be a good custodian of the Elder Wand, since Snape’s signature magic is purely defensive: when he has to force himself to attack or use Dark Magic, it’s only in order to protect others, then immediately dropped. "

― Lorrie Kim , Snape: A Definitive Reading