23
" He asks, “Is this remorse, Severus?” Snape doesn’t reply. He doesn’t understand yet what Dumbledore means. Instead, he says he wishes he were dead. (HP/DH, 678) He is quite sincere. His life is over. From this point on, if Dumbledore intervenes and calls on the most vital thing remaining in Snape—his love for Lily—Snape can start again, from the beginning, and have a second chance to do right. It is too late to protect Lily, but if all goes well, Snape can help spare the innocent life of Lily’s son, whom Voldemort will surely attack again. Snape cannot live for himself anymore; his heart is broken by guilt; he doesn’t feel deserving. But he gave himself to Dumbledore when he pledged “anything” in exchange for Lily’s protection, and Dumbledore sees a hope. If he calls on Snape to live for Dumbledore for the moment, to do as Dumbledore orders him, and keeps calling on the part of Snape that loves, keeps calling on Snape to do more and more for love and protect others for love, there’s a chance that this love can grow strong enough to sustain Snape so that he can find his own reasons to live again. "
― Lorrie Kim , Snape: A Definitive Reading
33
" After Dumbledore enters, Harry sees that “Snape followed him, looking into the Foe-Glass, where his own face was still visible, glaring into the room.” (HP/GoF, 679) Perhaps Snape is checking for magical confirmation of what he knows to be true: his renunciation of Voldemort is genuine. He is so young and new to double agency, at this point, that he still looks for reassurance, for external mirroring of his internal reality, especially since he has so often been disbelieved. As he gets further into his mission, as more lives depend upon him, he will have to learn to avoid or fool magical mirrors so they don’t give him away. There will come a point when he learns to hide his true self so deeply that he won’t show up in mirrors at all. "
― Lorrie Kim , Snape: A Definitive Reading