I read this book a couple of years ago now and it was one of the most satisfying books I have ever read.
It tracks the life of a husband and wife who settle in the fringes of the outback. It works through their hopes and aspirations, the birth of their children, their middle-aged disillusionment and their ultimate ends.
In point of fact nothing really happens in the book at all; these are just ordinary people, for the times. What does happen is that you are presented with an extremely powerful emotional picture of the main protagonists and their interaction with their environment. It tells us how the everyday, ordinary events these people experience turn them into what they are. The result is a gloriously truthful and unaffected portrait of humanity.
I don't know what the official rationale for the books title was, but what I think White is trying to say is that, here is man, occasionally glum, occasionally glorious, mostly mundane and of such stuff are we all made.
Read this when you finally get sick of all the fantasy heroes and heroines. Here's the real thing.