Its about puns, human nature, drinking and bars.
But most of all its about hope.
The people who find callahan's generally need help and they find it there.
Spider Robinson has been asked many times where they can find the bar in real life or how to get there.
His response has been. "You are standing in it." Meaning the help people need is there.
But all the book has shown me is that. Stories purely on hope and regaining it tend to depress me.