According to statements made in The Grapes of Wrath, what importance is anger in overcoming fear?

I think that anger is a necessary condition for social
change.  Steinbeck makes it very clear that anger is what allows social solidarity to
happen.  It is anger that changes what is into what can or should be.  Anger is the
motivating force, but Steinbeck argues that in order for it to be relevant and useful,
it must be directed towards some productive end.  Anger for its own sake is something
that is not seen as breeding social change, but rather enabling individual alienation. 
Jim Casy is an example of how anger can be productive.  Casy is angry at how the worker
is being mistreated by those in the position of power, and he channels his anger into
working with those who need his help.  Tom Joad is angry when he sees what his family
endures and in the critical moment when Casy is beaten and killed.  Through reflection,
he understands that his anger will be best served if he is able to carry out Casy's work
and broaden social solidarity in the name of transforming what is into what should be. 
For Steinbeck, anger is the key to bringing hope and redemption into the world. 
Steinbeck believes that when people get angry enough to demand and to fight for change,
it is here where they will be able to transform their reality.  This becomes the
critical statement that the work makes about anger.