What’s the key way in which Priestley explores the importance of social class in An Inspector Calls?

Priestly did not agree with the way the social class was and he believed that everyone in society was responsible for each other. He used the characters to show the unfairness of the class system, the obvious one being Eva/Daisy as it was due to her belonging to the lower class and not having and support to help her in each of the situation she found herself in. Priestly showed the "power" the upper class had mainly through Mr Birling in "sacking" Eva and Mrs Birling in not supporting her through the charity "girls of that class". He also showed social class through Edna, the maid, she spoke very little and followed any instructions given to her by the Birling's.

The key way that Priestly explored social class is in how Eva Smith is treated by each member of the Birling family and Gerald. In each situation, they could only treat Eva so poorly because she was working class and they were upper middle class AND they saw nothing wrong with what they did! (with the exception of Sheila - our hero of the play). Today, such treatment would be almost impossible because of law changes and societal changes.