[Samifer stops for a moment, placing a finger to his chin.] Here, let me show you. [With a snap of his fingers, he brings them both into the exact point in time where Dean is talking to Sam about being a monster because of the demon blood, all while Sam is trying to explain he's saving people, keeping them alive.]
You see, Dean. He was trying to do good, for you. But you... You didn't want to listen to him. Fast forward a little and... [Lucifer snaps his fingers again, Dean is in a hotel room alone, on the phone with Sam.]
[This is the point that Dean tells Sam that he thinks they should split up and stay apart, moment before Zachariah would send Dean 5 years into the future and see what happens during the apocolypse]
You see, Dean. Sam didn't want to be alone, but you left him. I'm here to bring forth the apocolypse, because our Father has given up on you creatures. You've failed him, and he's left Heaven. And now, I'm cleaning up his mess.