Why this book was written? What does the author want us to learn?

From the text, we can infer that the author wished to:

1) Impart information about how the Holocaust began.

2) Illustrate the way the Nazi regime so easily pulled people into its ranks.

One of the biggest questions people ask about the Holocaust is "how" it happened. How could so many good people accept Hilter's regime and its subsequent annihilation of millions of people? In writing The Wave, and experimenting with high-school students, Strasser illustrates the ease with which propaganda and a sense of belonging can turn a group into a force.

The Wave was written as a novel from a teleplay authored by Johnny Dawkins.