To Jimmy Novak, Claire was the world and all the stars in the sky. To Castiel, Dean is the world and all the stars that comprise the Universe.
Reconciling the two…is impossible. It’s impossible because Castiel, regardless of appearance or mannerism or voice, is not, nor will he ever be, Jimmy Novak.
Castiel sets off on this journey to right wrongs, to repay a debt to man who gave up his life in God’s name in order to help save the world. The problem lies in the fact that Claire doesn’t want to be saved. She doesn’t want to be saved because Castiel cannot turn back time and bring her father back. Claire learned how to survive, even if she had to cut and bleed and kill to make it from one day to the next. She gave up prayingfor salvation a long time ago. Her lack of faith dragged her down into the deep dark spaces that could never filled inside of her - the spaces where love and family used to be, the spaces where an angel’s grace filled her, only to leave her bereft. Claire stopped believing.
And then there is Dean. The one guy that Castiel has reconstructed the entirety of his existence around. The one guy that Castiel has rebelled for, bled for, died for, become God for. Everything, all of it, in the name of saving Dean Winchester. In Purgatory, Castiel made a choice - leave Dean behind because it was the only way to say him. And Dean learned how to survive - cutting and bleeding and destroying and opening up that pit inside of himself that tastes like hellfire and carrying on because prayer was his only saving grace. Every word he spoke to Cas in the distance between them was his salvation, even if Castiel failed to answer his call. It was faith that drove Dean to reunite with Cas, to escape from Purgatory. Dean never stopped believing.
Castiel sees Claire and Dean as his greatest failures because he couldn’t keep the promises that he made.Castiel promised Jimmy to take care of his family, and he failed. Cas promised Dean that he would come whenever he called, and he failed. What Castiel has yet to learn is that changing the past is impossible. There are no do-overs. Cas can’t take back abandoning Claire and Amelia, he can’t take back his rebellion, he can’t take back his betrayal, he can’t take back the destruction wrought under the guise of a false god, he can’t take back leaving Dean in Purgatory, he can’t take back leaving Dean at all. Castiel has yet to learn that every single one of the wrongs that he has attempted to right has led to more chaos.
Castiel doesn’t realize that the only thing he can truly do is to continue to live and to have faith.
These words from Claire’s mouth were a devastating reminder of Castiel’s perceived failures. But he must realize that changing the past isn’t an option - that becoming the visage of Claire’s father isn’t enough. He has to learn to build a new foundation with Claire as himself, as a friend, as Cas. He has to learn to love, to support, to guide, and be present for the sake of a human who has nothing. He can become the faith that she lost.
And then we come back to Dean. The one guy.
Back in Purgatory, Dean still had his faith in Castiel because it’s what kept him alive. Now, Dean is hapless - lost and alone amongst the wreckage of his own soul, fallen to his knees and broken apart in pools of blood and sorrow. Dean asked one last thing of Cas before he fell once again. One last favor - to kill him to save him from becoming a monster.
Castiel can’t keep that promise either. But he can make a new one - to save Dean Winchester in the way he needs to be saved the most.
To truly love - to form the deep impenetrable bond of devotion and mutual trust from a foundation of friendship and understanding - this is Castiel’s path. The reintroduction of Claire opened the door to Cas learning to truly love as a human in relationships based on human ideals where faith is something that is tangible beneath his finger tips.
Castiel, as an angel, has been given the gift of humanity. Cas has been given the opportunity to become the faith that is lost in the two people he could never truly save.
Castiel can become Claire’s faith in herself and gift her with the opportunity for a better life.
Cas can become Dean’s faith - his light through his own darkness - and gift him with salvation born from true love.
Failures of the past can only be used to learn from. Castiel has two lives to save, and their futures are shining with his immutable light.