The main theme, as far as the central story goes, is Saul's continuing lack of support aka betrayal of Carrie. Saul insists to everyone who questions him about this - Carrie's family and Quinn - that he has something bigger in mind, and he's doing this to protect Carrie.
But it's hard to see how that would work. Carrie's being locked up against her will, prevented from pursuing her drug-free approach which seemed to be working, doesn't ring true as a way of helping her. What does ring true is that Carrie missed the bombing of the CIA - something she feels terribly guilty about - because she was only "half there," as she says, due to the lithium.
Homeland being the complex show that it is, I'm inclined to give Saul the benefit of the doubt, but not for long. And if it turns out that he's really throwing Carrie to the wolves, we'll have witnessed a remarkable transformation of a good man, without sufficient motive.
Meanwhile, Dana continues to carry the story of the Brody family, with Brody himself still off the screen. The flirtation we saw in 3.1 with the boy in the mental institution Dana has been released from turns out to be much more, as Dana comes to him, they sleep together, and Dana professes her love of him to her mother. Dana's venting about her father and his lying is one of the best scenes in this episode, and one of the best moments from Dana on camera in the series. She continues to be one of the compelling centerpieces of this story.
With Carrie in mental custody, and Brody nowhere to be seen, Homeland has a lot of territory to cover to get these together. I'm looking forward to it.
And see also Homeland on Showtime ... Homeland 1.8: Surprises ... Homeland Concludes First Season: Exceptional