89
" ring. Like other powerful objects, such as the Sorcerer’s Stone, the Deathly Hallows are subject to one of Rowling’s cardinal rules: they belong to those who seek them not for gain, but to protect others. At different points in his life, Snape is each of the brothers in the tale. In youth, he was combative. After Lily died, he wanted to join her in death. But for his second chance in life, he has been keeping his true self hidden, not for personal gain but in order to protect others. According to Dumbledore, that is the essence of the Cloak of Invisibility, “the true magic of which, of course, is that it can be used to protect and shield others as well as its owner.” (HP/DH, 716) "
― Lorrie Kim , Snape: A Definitive Reading
93
" After all the precautions put in place for Lupin’s protection as a student, after all the special treatment, Lupin still led his friends into danger, out-of-bounds, at night, and visited Hogsmeade as a werewolf. Yet when Sirius nearly got him to kill another student, nobody was expelled; there is no evidence that anyone was even punished. The only consequence we know for sure is that Snape was “forbidden by Dumbledore to tell anybody” (HP/PoA, 357) that Lupin is a werewolf. He was forbidden to speak of his terrifying experience. His near murder, and his need to work through it by talking, were considered less important than Lupin’s privacy and, perhaps, Dumbledore’s chagrin. "
― Lorrie Kim , Snape: A Definitive Reading