Sam used to have a lot of scars before Castiel came along. Scars from knife wounds, from bullet holes, from a broken bone popping through his skin, from claw marks, from teeth, from scrapes, from punches. The angel had healed them completely and he kept on healing them. Though, sometimes Sam let his injuries scar.
Like the one he'd just received on his cheek from a werewolf. He wanted the scar as a reminder to be careful. He had been too bold during the recent hunt, and he'd gotten hurt because of it. It was his fault so he thought he might as well bear the mark.
There was already a faint scar on that cheek bone, just a tiny line of white against his skin that disappeared into his hairline. He'd gotten that one from getting beaten. But he saw that as his fault, too. He remembered feeling guilty about so many things at the time. Guilty for causing the deaths of some good people, even still harboring the guilt of starting the Apocalypse. So he kept the scar, thinking he deserved it.
A more faded scar was in his side just beneath his rib cage. It had been from friendly fire, from Dean. It was the one and only time his brother had accidently shot him. Usually they were both careful while firing their weapons in each other's presence, but adrenaline had been high, it'd been dark, and the shapeshifter they'd been fighting had gotten in between them, and it had been about to start tearing into Sam. Dean had panicked and he'd fired. It had saved Sam's life, but gotten him severely wounded in the process. Sam hadn't meant to keep the scar, didn't want Dean to see it whenever he got too hot while sparring or working out and he had to take his shirt off, but it didn't bother him, didn't plague him with guilt like it did his brother. So he usually forgot about it unless he caught a glimpse of the pink, puckered flesh while showering or looking at himself in the mirror.
There was a scar in between two of his toes on his left foot just from stumbling while running through the woods in the dark. Their dad had trained them in traversing tough landscapes at night without a flashlight, but sometimes you just messed up. Sam had fallen, and the jagged edge of a rock had gone right into his foot. He kept that scar there because it was of no import to him. It seemed rude and ungrateful to ask Castiel to heal something as trivial as that. Nothing fatal, nothing serious, just an accident.
Now Sam was reminded of these scars as he looked at himself in the mirror after just having gotten out of the shower.
It wasn't often that Sam actually took time to look at himself, but he had decided to do so now. He didn't like it. He looked at himself and he saw the scars, the ones on his body, the ones that had been healed, and the ones that were inside, untouchable, unreachable, permanent no matter how many times the healing hands of an angel touched him.
Inside him was his soul, and that hurting thing was nothing but scar tissue.
Sam knew scar tissue was tougher than the skin that had been ripped apart, but it could still hurt, depending how deep it went. And these scars ran very deep, deeper than anything he could wrap his head around sometimes. Some days it seemed it was all he was.
Now, Sam ignored the scars on his skin, the scars that had once marked him. Instead, he met his own gaze in the mirror, and that's where he saw the scars. That was where the worst of it was. That was Hell. That was himself.
Sam was all scars inside.