Episode 4 'Shindig' is about the differences between the lifestyles of Mal and Inara.
Inara is a companion - high class prostitute - which seems to be a legal and respectable occupation. Mal - who is a unquestionably a criminal (albeit one that the audience is urged to cheer for) - looks down on Inara's profession. The Bible Study on the Youth Ministry Blog relates this to the Biblical story of the one who said 'Friend let me remove the speck from your eye', whilst ignoring the log in his/her own eye.
Note to self - I would like to reflect further on the ease with which the audience (including me) can excuse the criminal aspects of Mal's life.