" Dumbledore won’t tell Snape that the ring is set with the Resurrection Stone or that there are such things as Horcruxes. He doesn’t want Voldemort to learn about the Deathly Hallows through Legilimency on Snape, and he certainly wouldn’t want to tell Snape about Horcruxes and have Voldemort discover that Snape knows this secret "

― Lorrie Kim , Snape: A Definitive Reading