Parallel to Dean’s death, Castiel smashed the Angel Tablet. This symbolic "breaking" of the most powerful instrument in the universe mirrored the breaking of the Winchester bond, which many fans consider the true heart of the show. The Resurrection: "Open Your Eyes, Dean"
The episode's final two seconds provided perhaps the most shocking visual in the series. As Sam tried to summon to make a deal for Dean's life, the King of Hell was already in the bunker, monologues over Dean’s corpse about the "true" story of Cain. Watch www xrysoi se Supernatural S09E23
In a powerful act of self-sacrifice, Gadreel blew himself up to free Castiel from Heaven's dungeon. This act convinced the other angels of Metatron ’s deception and allowed Castiel to finally expose Metatron's true, narcissistic nature over "Angel Radio". Parallel to Dean’s death, Castiel smashed the Angel Tablet