Fences
One of the main themes in the film is that of boundaries, or fences being created to keep people away from each other. Everything has become his or hers or mine to Jack. In his mind there should be no separation between people. Thus, him cutting the fence at the opening of the film, Paul being in prison, the busy roads he must attempt to cross all become fences to the old west, a place Jack still lives in where life is simpler and all connected.
Old West vs. New World
The opening shot tells us everything we need to know about this theme. We see planes flying overhead as Jack saddles up his horse. We can discern that there is a clash between the old way of living, the way of the cowboy that Jack leads, and the new and fast-paced world that exists around him.
Loyalty
Loyalty is a major theme of this film. It's the reason that Jack is being chased down by the police. He is loyal to his friend, Paul and he believes he's doing the right thing by breaking in to break him out. But, Paul has grown, he's loyal to his family now. He has more to live for and we see how loyalty changes into something more as life goes on.
