I think that the mountain girls represent repeated mistakes. After meeting the first mountain girl and sleeping with her, the arch priest has to avoid her, because he made promises that he could keep. But, it seems like he keeps running into the same "problem" over and over, he gets kind of lost and cold and hungry, and then he finds another mountain girl and expects food, shelter and sex from her because that's what he got from the other mountain girls. After the first girl, the others don't react so well to his expectation that they bring him home with them, however, they all do it. When he meets the girl who is hideously ugly he still flatters her to get what he wants, but she refuses him unless he actually has what she asks for. So, what the reader and the arch priest must learn from this, is that one cannot make assumptions about the reactions one person based on the reactions of another to the same situation.

The battle between Carnal and Lent symbolizes the fight against temptation. When people are asked to give up things they enjoy (food) for a greater purpose, like religion and Lent they struggle. The literal "food fight" in the text, comically,  represents the internal struggle that people have during Lent.