Elizabeth's guilt about her frigidity to Proctor makes her lie to the court about his adultery, again linking him to the Devil.
Other human "flaws" which are manipulated by people in the court system are vengeance (Abigail and the Putnams); jealousy (Abigail and the Putnams); fear and hysteria (the girls in the court); ambition and power (Abigail and Danforth); and greed and lust (the Putnams and Abigail). Indeed, it seems nearly the entire book is overrun with evil characters and evil intentions.
In a sense, Miller is asking the reader whether evil naturally exists in human nature. His ending reveals that good can triumph over evil, but at a great cost, and that evil is insidious and ongoing and can't be easily eliminated. Although some ray of sunshine is evident at the end of the play, both figuratively and in the stage directions, there is still a sense of overriding evil.
By creating this overriding evil in the play, Miller positions the audience to take sides in this most basic of conflicts: good vs. evil. Just as these sorts of conflicts are evident in their everyday lives, a reader of any time can apply it to The Crucible, take sides with the characters and be drawn into the text. And to be drawn into the text makes the text relevant to the reader - a reader of any time.
The characters themselves also help to make The Crucible the timeless play it is. By creating some definite characters who we know are evil or are good, we can apply them to people we know in our own lives. For example, the characteristics of Rebecca and Francis Nurse - the two characters who represent all that is good and honest in the play - could be subconsciously attributed to a loved family member. On the other hand, Abigail Williams - an evil and manipulative slut - could be read as an ex-girlfriend or a vicious warlord.
Since these characters are so definite, and we can so easily draw parallels between them and people in our own lives (whatever time we live in), the text becomes relevant to us, because it is people we know who are "in" it.
