How can John Proctor's death serve to illustrate the meaning of the concept of The Crucible?
Proctor's death represents a couple of levels of meaning that can apply to the play, in general. Miller deliberately designed the drama to center on Proctor. He is to be the embodiment of the tragedy of Salem, the entire premise of the "crucible." Indeed, Proctor's test under which the most searing of heat is applied resides in what he values. Proctor's death makes it clear that one's name and reputation is the only constant in a world of complete mutability and change:
Because it is my name! Because I cannot have another in my life! Because I lie and sign myself to lies! Because I am not worth the dust on the feet of them that hang! How may I live without my name? I have given you my soul, leave me my name!
Proctor's death also demonstrates how sacrifice for social change is an inevitable condition in the modern setting. Proctor reverses course in his "confession" because he understands how his evasion of sacrifice will be twisted and manipulated by those in the position of power. He understands that while he is no martyr, he wishes to be in some level of control over his name and identity. In a setting where the corrupt have ascended power, Proctor understands that compliance with such authority is a form of emboldening it. It is here where his death represents one of the strongest form of dissent and protest. Proctor's death is the embodiment of "the crucible," the test to which individuals are to face in conditions where injustice masquerades as justice.
I think that Proctor's death also represents a personalized form of "the crucible," as well. Proctor's death is the first time he acts with complete confidence and a sense of self- assurance in his marriage. His action is done to ensure that he can be seen as a good husband to his wife. The "goodness" to which Elizabeth speaks at the play's conclusion is something that only arises from his death. Proctor's death represents the ultimate in sacrifice that a husband makes for his wife, his marriage, and the sense of dignity with which spouses must see one another. It is another "test" that burns marriages if one fails it. It is one that Proctor's death ends up upholding his at the end of the play.