QUOTE : The debt he incurred to Dumbledore is an emotional connection: gratitude, a form of love. This gives Dumbledore the closeness to suggest to Snape that he begin a second chance at life. Without that closeness, nothing would have tethered Snape to life once Lily died. Everything Snape does in life after this moment is extra. It’s a gift from Death. Snape is infinitely stronger because he doesn’t fear Death after this. He was willing to meet Death at 21; at Dumbledore’s offer, he goes under an invisibility cloak of sorts, takes on a life of double agency, to see what he can accomplish before he takes off the cloak and meets Death again. The two requests Snape made because of love for Lily are what created enough power to protect Harry Potter