Pithy dialogue consists of concise and forcefully expressive language. Basically what this means is that the words spoken by the character, or person, are meant to evoke emotion from the one they are speaking to or from the reader.
In regards to Peace Like a River, language and dialogue is important when examining Jeremiah. Suddenly turning to spirituality, after being thrown by a tornado, Jeremiah realizes the importance of why things happen as they do. The following quote provides one examples of Jeremiah's pithy dialogue.
"Baptized by that tornado into a life of new ambitions."
What this means is that suddenness of the tornado justified the suddenness of making a new life for himself. The language is very concise and expressive--thus making it pithy.
Another example by Jeremiah's pithy language is a conversation which takes place between Jeremiah and his son, Reuben.
"God told me you were in trouble."
"Out loud? Did you hear him?"
"Nope, not out loud. But he made me run, Reuben. I guess he made me figure it out that way."
Here, Jeremiah's language offers very concise words and emotion again. An engaged reader can picture Jeremiah with his hand on his son's head recalling the day of Reuben's birth. The image created by the pithy language proves it to be expressive of the memories they are sharing together.
Perhaps the most compelling example of Jeremiah's pithy language is provided when he is holding Reuben's new born body and commanding it to breathe.
"Reuben Land, in the name of the Living God I am telling you to breathe."
This is, by far, a very concise and forcibly expressive statement. Jeremiah could not have said what he wanted to say in any other way.