Disclaimer: I don't own Sam or Dean, or indeed Pastor Jim, Missouri or Layla. But I'm very fond of them.
Author's Note: I've messed around with angel lore here. I'm also a little unsure about the ethics of having God as a character, but my relationship with God is both complex and loving and I think She'll be okay. As always, apologies for any Australian spelling. I am aware that Sam and Dean live their life in American English, but I write in Australian.
There is evil in the world, real evil. There are demons and they walk amongst us. The Winchesters know this. They've been fighting evil for decades.
But here's the thing. Where there is evil, there is also good. And just as demons walk the earth, so do angels.
Angels. From the Greek, angelos, messenger. Messengers from the good that many call God. People who for a day or a season or a lifetime, knowingly or unconsciously, bring God's message to humanity.
The ones we know by name are usually men: Shakespeare; Mozart; Gandhi; Bonhoeffer; Mandela. But angels come in both sexes, all races, all classes. The Winchesters have met three of them: a preacher man called Jim; a motherly woman called Missouri; a beautiful blonde called Layla. People who have shared with the Winchesters God's message of faith, hope and love. None of them knew that that was what was happening. One thing most people agree on is that God works in mysterious ways and uses the strangest and most unlikely people for Her purpose.
In the fight between good and evil God has used the Winchesters. God's purposes are mysterious, and this hasn't always seemed to go well.
"No one has greater love than this," said the One who was both messenger and message, "to lay down one's life for one's friends." The Winchesters have this love. Each is willing to give his life for the others. For John and Dean, this led to deals with demons that sacrificed not merely their lives but their souls.
Sam Winchester doesn't follow their example. He doesn't summon a demon and make a deal. Instead, on the night that Dean's year is up, on the night his brother's soul is forfeit, Sam sits next to Dean in the church that was once Pastor Jim's and looks up at the cross on the wall. And, without being aware that he's doing it, he offers himself to God. Heart and soul, body and mind, he offers everything he is, everything he has, in exchange for his brother's life and soul.
Demons possess people. Angels possess people too. Not so often. Demons enjoy violating humans, they enter without permission, imprison people in their bodies, use them any way they wish. Goodness, the unmediated power of God, only enters people with their permission, when people are willing to completely and irrevocably sacrifice themselves for those they love. It doesn't happen often, and when it happens we remember their names, even if the forms change and the stories become distorted: Gabriella; Michael; Raphaella; Jophiel; Uriel. We call them archangels; not merely messengers but personifications of the goodness of God. Angelic possession is rarer than demonic possession. But it happens.
So as the stars go out, the moon disappears, the night turns black, and the hellhounds are heard on the threshold, Samuel Winchester stands up. He bends down and kisses Dean on the forehead. Then he walks, slowly, as though in a procession, up the aisle to the door, and as he walks he changes, until he seems to Dean to be clothed in fire, enveloped in white light. He lifts his right hand and there is a sword in it. Michael once wielded that sword. The hellhounds recognise it. There are seven of them, one of him. But he has all the power and they all know it. Gracefully, without a single wasted move, Samuel kills them. Dean, watching, thinks that it is like a dance. The sword pierces their hearts and they melt away. Then Samuel speaks.
"The deal is done. You came for him, but you couldn't take him. The deal is done. Dean's soul is free."
For a moment there is silence, absolute, heavy with meaning. Then the stars are back, the moon is out, and Samuel is suddenly just Sam again, turning to his brother for comfort and reassurance. And the two men stand in the middle of the church, arms around each other, holding each other, in a place that has been for a moment illuminated with the presence of God.
If there is demonic possession, then it only makes sense that there is also angelic possession. And as for Sam Winchester becoming for a moment an archangel – well, in the world of the Winchesters, stranger things have happened.