In the beginning of the book you said there would be a big idea of the story is fair is foul and foul is fair. This is said by the witches at the beginning of the play and this saying is a theme of the whole play. The witches say this mostly when they are doing chants and making spells so the meaning is obviously very involved with the witches and they are aware of meaning.

I believe this is the biggest idea surrounding the book because though the witches are not in every scene the witches are the whole reason the story is happening. What they said "Fair is foul and foul is fair" is basically showing what a normal man would think is foul is what the witches think and vice versa. Most people thought the killing he was soing is foul but not to the witches who told him to do it.