This quote is from Arthur Miller's comments before the action starts in Act I.
If you look at the context, the quote is actually talking about how the people in Salem during those days could best protect themselves. And what they needed to protect themselves from was the Indians. The quote is followed by
The edge of the wilderness was close by. The American continent ... stood dark, threatenening... for out of it Indian tribes marauded from time to time.
However, in the context of the play, you can argue that Miller is trying to foreshadow or refer to what is to come. During the witch trials, you could see the quote in two ways:
- You were only safe if you stood with the court -- in unity.
- The only way true safety could ever come about would be from the town standing up to the court.
This quote, provided by Miller prior to Act One, anticipates the dangerous mob mentality that will soon settle over Salem and the persistent persecution of individualism within the community. "Unity" within this context means "conformity"; in order to stay alive in this time, one was required to fall in line with the predominant beliefs: the Puritanical values and the system of prosecution (and persecution) that targeted individuals. Safety was in numbers, and the numbers were certainly stacked on the side of the law and religious conservatives. To stand against the courts was to put oneself at risk of later being confused; dissent was not welcome.
This quote also outlines the greatest mistake made by the residents of Salem: turning against each other. By betraying their peers, friends, and neighbors with accusations of witchcraft under the watchful eye of the courts, the people of Salem create a culture of mass hysteria, one that ultimately destroys the community. After so many members of the community are either executed or imprisoned, many children are left orphaned, wildlife roam the roads, and crops are destroyed by rot. With the town in shambles, those left free have no central sense of "home" left to protect or even live for.