After the apocalypse aka the great war between Heaven and Hell ended it became silent in both teams .Many more years had pass and Gabriel the archangel had enough of boredom so he goes down to the human world and he saw how peaceful and sweet Crowley and Aziraphael are and quickly thought that,"If God knows what is happening now and just turning a blind eye and if i follow my heart will i be too known as a traitor" after that Gabriel disappeared to go to heaven not knowing Crowley saw him and smirk because he knows a new chapter will begin.