There is a definite difference between a theme and a moral. A theme is more of a one-word description of a thread that is discussed throughout the entire play. For example, "mass hysteria", or "integrity". But a moral is usually a one-sentence lesson that the story tries to bring forth. So if you are looking for a theme, what are the major issues that are discussed in the book? I listed two above-mass hysteria, and integrity. The entire book is about how a group of girls create mass hysteria in a small town, and the effects that hysteria has on hundreds of people. So, mass hysteria is definitely a main theme in this play. Integrity is another theme, which is mainly exemplified through John Proctor. Though a flawed man, he demonstrates integrity as he confesses his sins, tries to save his friends, and ultimately gives his life so that he doesn't have to lie. So, integrity, human courage, or bravery could be another major theme of the novel.
If you are looking for a moral or lesson, then you have to think about what message you feel Miller is trying to get across, in relation to the themes. For example, "mass hysteria is dangerous and is often not combatted by logic." Or, "mass hysteria is often an outlet for jealousy, greed, rage, insecurities, guilt and weakness." In relation to integrity, a moral could be, "Integrity is the most important human quality that must not be sacrificed, no matter what the cost." So, those statements go along the lines of being lessons or morals, but also tie to the theme.
I hope that helps a bit; I provided a link below that will lead you to more thorough discussion of theme and that should help also. Good luck!
If you're interested in the theme of hysteria in The Crucible, watch this short video:
It seems to me that the main theme of this play is the effect of irrational fear upon society. Miller did, of course, base his treatment of the Salem trials on the effects of McCarthyism. McCarthy played on people's fear of communism, and the fear that there were invivible communist infiltrators working their way into positions of authority in American society. He worked on that fear in a manner calculated to arouse irrational, emotional responses in the public instead of reasoned reactions.
In the Crucible, people are subjected to fears of their neighbors and fears of unseen influences working among them, just like the fears McCarthyism fostered in Americans.
Miller used the standard history textbook versions of the Salem trials as his basic setting, and then used the normal sort of literary devices to expound upon this theme. Of course, it is a work of fiction based loosely upon an historic incident. The actual Salem trials were far different from the situation in the play. There was certainly an irrational reaction based upon fear displayed by the public and the magistrates in Salem, Andover and other locations in Massachusetts at the time, but an examination of documents contemporary with the trials (not Robert Calef's later and largely untrue criticisms or Upham's atrocious 'history' of the trials) reveals a society in panic, but not motivated by malice. McCarthyism was a malicious and ambition-driven political incident.
While there are certainly many themes to this story, the main theme is best identified by Miller himself. Since the first production of the play, audiences have responded to the connection between the witch trials of Salem, the center conflict of the play, and the McCarthy trials of the 1950's. Miller calls attention to that connection himself in this article from 2000.
Arthur Miller, "Are You Now Or Were You Ever?"
Saturday June 17, 2000
"It would probably never have occurred to me to write a play about the Salem witch trials of 1692 had I not seen some astonishing correspondences with that calamity in the America of the late 40s and early 50s. My basic need was to respond to a phenomenon which, with only small exaggeration, one could say paralysed a whole generation and in a short time dried up the habits of trust and toleration in public discourse."
The textual evidence of Miller's message exists in the parallel of the trials themselves, but also in the long sections of introductory information Miller added to the publication of The Crucible script. While these sections would not be part of a stage performance, the inclusion in the printed form shows Miller's need to emphasize his own theme. These sections spend time introducing the town and focusing on the community. He describes the townspeople as petty, suspicious, and hypocritical. He makes a point to say that they have a “predilection for minding other people’s business.” All of this information is provided before the main conflicts are fully developed. Miller is pointing the readers of his play to the proof that it is the downfall of the community - not specifically John Proctor - that is the important thematic event of this story.
The play is about not conforming to society's notions of right and wrong and being an individual capable of making one's own decisions about morality. In essence; what Proctor does through the play symbolizes the whole meaning.
In the final scene in jail, Proctor achieves heroic stature when he decides that his life is worth less than his duty to the truth. His claim to personal happiness is less important than the truth that the whole community—and history—needs, and he overcomes his previous, somewhat contrived flaw (adulterous lust). Because of Proctor’s act, Arthur Miller implies in an epilogue to the printed play entitled “Echoes down the Corridor,” “the power of theocracy in Massachusetts was broken.”
A good example is in act 1:
Parris—now he’s out with it: There is a party in this church. I am not blind; there is a faction and a party.
Proctor: Against you?
Putnam: Against him and all authority!
Proctor: Why, then I must find it and join it.