There's also the incredible chemistry between Jensen and Jared. Sure, that happens every week, but considering one of them is a totally different character this time, and the fact that these two have such a stunning exchange makes the scene that much more extraordinary. It's not only far better than the clever editing with the Dean/Future Dean scenes, it's one of the best scenes these two have ever done. After 86 episodes, that says a lot.
The scene primarily works because Lucifer stays in true haunting form (with one fine looking suit to boot) while Dean lets his human side show. That is the most important element of that whole scene. When Lucifer/Sam gives his speech about Dean’s choices, Dean weeps. No single tear rolling down this time, both eyes are pooling. That’s the human thing to do. It isn't weakness, it's showing character. It's showing true compassion for humanity and for his lost brother. It overshadows all the false sympathy Lucifer throws at him and sends a message that there’s hope for salvation through human weakness.
Zachariah wastes no time in pulling Dean back and giving him another chance to change things. Say yes to Michael, before the virus begins, before Lucifer gets to Sam. Something clicks during that long, reflective pause. Future Dean, even though he begged him to say yes, knew he’d say no. Lucifer told him whatever choices he made, it wouldn’t change things. Dean figures out he has to say yes in order to save the world. But not to Zachariah. “I learned a lesson alright. Just not the one you wanted to teach.” He realizes what set off these events wasn’t him saying no to Michael. It was him saying no to Sam. Lucky for Dean, Castiel is good at showing up for appointments on time. It’s time for Dean to right his wrong with one phone call.
The grand reconciliation of the brothers isn't all hugs and smiles, as it shouldn't be. They are finally taking a crucial step forward, but the past still lingers. There will still be differences, there will still be mistrust. That, too, is a very human concept. However, they are both wise enough to know that while they are each other's weakness, the consequences of them apart are far worse than when they're together. “The point is, maybe we are each other’s Achilles heel, they’ll find a way to use us against each other I don’t know, I just know we’re all we’ve got. More than that, we keep each other human.” The premise for the episodes to come is now established. “We make our own future.” "I guess we have no choice." Interesting how that was the premise at the start of the series as well.