As a living man, Severus did not believe in God. He had seen enough to support his agnosticism. He had cast too many Unforgivables, endured too many beatings, witnessed too many torturings to believe in an almighty, loving deity. Every time the Dark Mark, the testament to his faults and failings, burned on his arm, a piece of Severus's humanity was engulfed in flames until completely lost in a pile of what-used-to-be. Before he would follow the call, Severus would reminisce, muse, concentrate, on his past for a fleeting amount of time and wonder, almost childishly, how his life had regressed so much to place him there, at that moment, answering to the Dark Lord.
As a young boy, Severus had never heard of love. His parents did not do wrong by taking the images of caring and adoration out of his mind; they had never allowed for any such feelings to be originally placed there in the first place. Never once did his father extend a loving arm to his mother to caress her, but instead Severus saw that arm as a device, a tool that was used to punish him or his mother. It would slap, punch, pinch, strangle, that arm that could never emulate passion. Severus did not understand affection, but there was no doubt in his mind as to what fear, loathing, or pain were.
And then he saw her, gliding through the air on a small swing set, spinning on her feet with her sister, their hands holding tight, laughing so that her entire face lit up in the sunbeams. When he was eleven years old, Severus Snape fell in love with Lily Evans.
As a growing boy, Severus discovered the power of love. That same smile of the girl did not just illuminate her face, but also gave light to his mentality that had been darkened for so long by his father. Her soft hands would wipe away the tears he shed to purge his body of the sins his family had introduced him to. Her silken hair blowing in the wind would carry her scent to his nose, and he would do anything to keep that smell with him. She had a profound impact on his soul; she was his only light. But the darkness within him suffered her for only so long, and as Lily and Severus grew older, the morbid components of his past and present overcame the light she provided him, and he lost her.
As a lonely man, Severus rejected God. On his knees in the bedroom of the once Sirius Black, again attempting to cleanse his soul through tears, he clung to the memories of her as tightly as he held onto the parchment carrying her name. He did not understand how God could take her from him, from the world. She was the embodiment of innocence, purity, love. He tucked her signature inside his robes, next to where his heart once was, and walked away.
As a dying man, Severus found God. He stood listening to Voldemort explain the failing of the Elder Wand and tried to get to the boy. When his efforts were rejected, he had no source to turn to for aid, no way of contacting the boy. Please, God, he found himself repeating, Please, God. Please bring him to me somehow. Please God. Please God. I have failed in everything else. Please God, help me keep from failing Lily again. The snake attacked him and he felt the remains of his heart break, aching with disappointment in himself, his life, his past, his actions. Please God. Please. And then there were the green eyes above him. Love, he thought, Lily, I could have saved you. As realization dawned, as he understood that his final, his only prayer had been answered, that the boy had found him, Severus exalted. "Take…it….Take…it…" He released his memories of Lily, of his life, of Dumbledore's secrets. As his blood began to slow, Severus basked in the few memories he had of his love, of her beauty and astounding grace. "Look…at…me," he begged. Lily. Thank you God.
"The hand holding Harry thudded to the floor, and Snape moved no more."
- J K Rowling, Harry Potter and the Deathly Hallows