Elizabeth actually learns many things in Arthur Miller's The Crucible. Her husband John had an affair with their former servant Abigail. Elizabeth finds out about it, confronts John, and then stays with him. Clearly she learned how to forgive. Another thing Elizabeth learned is that, despite his moral failing, she loves her husband very much. She understands and loves him enough to let him die at peace with God. She learns that life isn't fair and that jealousy is a powerful emotion, for she is unfairly punished because of a false accusation made by Abigail. Finally, among other things, Elizabeth is able to understand it was her own insecurities which prompted her husband, at least in part, to temporarily forsake her. The last time she speaks to John she asks his forgiveness, saying it's a cold woman who prompts her husband to lechery. This is an epiphany of sorts, and she is willing to take her share of the blame for John's adultery. This story is, indeed, a journey of self-discovery for Elizabeth.
The previous post was quite strong. I would merely add that Elizabeth learns where value should be placed in the dynamics of a relationship. At the start of the play, she places value on the transgressions that John committed. It does haunt her and she cannot seem to overcome it. Yet, as the play progresses, and the situation in the town becomes more and more painful, Elizabeth understands that frivolity and silliness of such a transgression in the larger scope. When she is forced to lie to defend her husband and then also has to endure the fact that he is willing to die for his name, as well as the embrace of this reality in losing her husband for his name, she learns a great deal. Elizabeth understands where true value lies, and where primacy must be placed in a larger configuration. It is through this process where she becomes a transcendental figure and is one where she, and the reader, understand what defines importance.