“Swan Song” sets up its emotional climax from the very beginning of the episode with the prophet Chuck (Rob Benedict) — who’s actually God — writing about the history of the Impala. He calls it the “most important object in pretty much the whole universe,” leading into a shot of Sam sitting on its hood, drinking a beer. Already, we’re getting into the emotional weeds of Sam and Dean’s relationship, as Dean tells his brother that he’s on board with the plan that will almost certainly get Sam killed. But hey, sharing beers next to the Impala is about as happy as these two get. It’s a last sweet moment.
Partway through the episode, Chuck takes us back to the Impala and shows scenes of how the Winchesters have left their mark on it — the Army man in the ashtray, the Legos in the vents — to really hammer in the idea that this car is their home. We’ve seen them in it countless times over the previous five seasons, and now all those small moments add up to a real tearjerker of a scene.
When Lucifer possesses Sam, he kills Castiel (Misha Collins) and Bobby (Jim Beaver) and then proceeds to nearly pound Dean’s face in against the side of the Impala. However, something catches his eye: the aforementioned Army man. In a flash, memories of their lives in the Impala play across the screen and give Sam the strength to take control of his own body. He says goodbye and sacrifices himself to Hell to save the world. It’s heart-wrenching at the same time that it’s satisfying — their plan worked with the power of love and family! But that also means Sam dies and has to spend eternity in Hell.
Many fans see everything post-“Swan Song” as a turning point for “Supernatural,” and even regard it as a soft finale. It’s the top-rated episode of the entire series on IMDb, and for good reason.