Reading this play as a moral tale, there are two particular themes that stand out. The challenge to an individual's integrity stands at the heart of the play as does a warning about abdicating responsibility for behavior and opinion.
In the play, individuals are challenged to admit mistakes, swallow pride, and act according to conscience. Proctor, Hale, Abigail and Mary Warren each face this challenge. Failure leads to severely negative outcomes in the play, as Hale's initial insistence on his own opinion leads to the arrest of Elizabeth and later John Proctor. Similar arguments can be made as to the results of Mary Warren and Abigail's lack of ability to stand by the truth and act according to conscience.
Only conscience and integrity can result in moral behavior. This is a central part of the play's commentary on behavior.
When Mary Warren and Reverend Hale fail to act with integrity they are bowing to the power of the group (or mob). In doing so, they attempt to relieve themselves of responsibility for their actions. This pattern of thought and behavior cannot have lasting success as evidenced by Hale's despair at the end of the play.