It's layered, complicated plot with it's satire and philosophical context rises many questions. The novel consists of wizards, talking cats and flying pigs but at the same time it reveals a dysfunctional society. The paranoia, the fear of the police and the senseless arrests are common in this book and can be connected to the time of it's creation. The frequent, unnamed fear that bubbles beneath the surface within the characters mirrors the oppressed Soviet society in the 30's.
The really interesting aspect is that the Devil isn't the true evil in the book. The true evil lies within people, and Woland just brings it out. Bulgakov reveals man's inner nature in an exceptional way. Human flaws such as greed and selfishness destroy the characters. Had they been able to resist the temptations, they would have made it. It takes people to build a dysfunctional society. The author shows how easy people are manipulated and affected by money, for instance.
The book deals with contrasts such as good and evil, courage and cowardice, belief and denial, and freedom and imprisonment. When people speak their mind they end up at the psychiatric ward. This symbolizes the oppressed people in the Soviet Union in the 30's. Being free wasn't a choice in such a society, and it required for Margarita to become a witch to be able to brake the rules. The novel also contains the concept of atheism during the time of its creation, and the significance of every man's right to believe.
Something interesting and worth speculating about is the true identity of the Master.