John Carradine did not receive an Oscar nomination for portraying Jim Casy in The Grapes of Wrath.
In the scene Carradine is rather outstanding in just how much insight he allows into the character as he shows both the past and the current state of the man. In the moments where Tom calls upon Casy's old days as a preacher Carradine suddenly realizes a man truly in his element as a man. In the way he moves so unusually it seems as though he is being motivated by the lord himself in his strange though quite spirited way he moves and speaks when reacting an old sermon. There is an extra bit of showmanship so to speak in this moment, as a memory of the past, because something that's so effective about Carradine's performance is the way he acts which is peculiar though works extremely well in realizing the character. That is that Carradine always portrays this certain quality that Casy has never stopped being a preacher exactly, in that he's just never lost the manner in the way he speaks and behaves. What's so remarkable is the way that Carradine is able to tread this fine line for the character that on one side his behavior seems like it could be that of a man whose half mad, or it is of a truly righteous man as there is something otherworldly in Carradine's portrayal of Casy.
Carradine captures this certain way for the character that is essential in that he makes every line of his absolutely work no matter how stylistic it may be. Anything that Casy says seems wholly honest through Carradine's delivery. Carradine makes nothing one note about this and through this even is able to allude to what lead to Casy's loss of faith. In his early talk with Tom he discusses his relationship with women, and Carradine through the enthusiasm twists his state as a preacher as it is not a religious sort of pleasure he felt when causing these women's, ahem, spiritual awakening. Carradine is able to suggest this misuse as a weakening of sorts, as it was obvious not wisdom he was giving them, and with that as Casy explains he gave up preaching due to not knowing the answers there is a resigned melancholy about. Carradine presents to be a man who no longer has a place as he still has never lost the preacher's mindset, that to be looking for something else, something more perhaps, which keeps him a distance from being just man, while also being too unsure of himself to be what he was meant to be.
As the film progresses Casy ends up going with the Joads in their journey to California to find some sort of prosperity and everyone is stuck in a certain mindset looking for a better life except Casy who comes along as well. Casy says basically that something is calling for him, and Carradine begins to portrays a spiritual re-awakening as he begins the journey with the Joads. Carradine is not given considerable individual focus in these scenes, yet if you watch him within them he adds a great deal to the power of the them, even past simply the vibrancy of Casy due to Carradine's portrayal of him. As the Joads suffer hardships or hear of the troubles of others Carradine's reactions are tremendous in the way he shows Casy taking in each story, and in a way each seems to strengthen his faith once more as though he's beginning to see his path once again. Casy is eventually separated from the Joads though Tom finds him again being part of a group of men leading a labor strike. The end of Casy's journey is powerfully realized in this final scene as Carradine creates this sense of enlightenment as Casy seems to be preaching the truth again, though a different truth than he had known before. The quick exit of Casy is made especially heartbreaking as Carradine makes into a shining light being snuffed out in a instance. This is a great performance by John Carradine.