When a teacher or professor asks for the "main idea" of the book, they want you to speak of the main theme. The main theme for the book Timebends is Miller's disillusionment with American society and, especially, with the theater culture. It is not the definitive biography of Miller, but a good representation of his life just the same.
In this literally time-bending biography, Miller laments a time when theater was what it should be. The title is reflected in one of his comments:
[Note the] imploding time ...moments when a buried layer of experience suddenly surges upward to become the new surface of one’s attention and flashes news from below.
Put simply, the theater culture is dependent on money instead of craft. Each playwright is at the mercy of his producers and critics. Miller laments this to no end. Producers control the money and, in fact, whether the play will even exist in society. Critics control the outcome of that play as well as future plays. The former is ruled by greed and the latter is ruled by gossip. As a result, Miller says this:
[America is] devolving into a mania for the distraction it called entertainment, day-and-night mimicry of art that menaced nothing, redeemed nothing, and meant nothing but forgetfulness.
In other words, Miller is lamenting a time when theater was real. Now it is simply used as an escape from life where people only want to be entertained and not taught. It leads one to see the truth if you take a look at the upcoming summer blockbuster movies. A true testament to Miller's "mimicry of art," many of them are simply re-told stories that the producers know will make money.
In Timebends, apart from simply society disillusionment, Arthur Miller reveals the importance of character and what the reader/watcher should retrieve in regards to these important characters.
A character is defined by the kinds of challenges he cannot walk away from. And by those he has walked away from that cause him remorse.
A character, to Miller, is meant to be more than just entertaining. That character should TEACH... that character should show the importance of challenges and the result of dismissal of those challenges. Regret is of utmost importance.
In conclusion, I must stay that I was fortunate enough to see Arthur Miller speak in person at Furman University in the early nineties. Apart from being bedazzled by seeing one of the great dramatists of our time, I was also struck by the negativity and pessimism that dots his autobiography, Timebends. Still, he rages against the machine and achieves success by the following:
I could not imagine a theatre worth my time that did not want to change the world.
Change the world, you did, Arthur Miller. Thank you for your amazing contributions to American drama.