Books of chivalry usually note the adventures of these knights and the morals and the values they uphold. Don Quixote who has regained coherence (as he lay dying) makes note to not have someone in his niece's life who is also plagued by these fantastical adventures. I found this paper, which was a lecture, about courtly love and how the values of chivalry influenced the knights (their love languages, their time away from wives etc) . I found it interesting as I'm sure that Don Quixote was thinking of the knights in his books and how they acted towards their lovers and how himself acted as the books took ahold of him.

https://chaucer.fas.harvard.edu/pages/courtly-love-and-chivalry-later-middle-ages

I find it interesting that they are burning books. I think the image and overall meaning of books being thrown into fire (to erase what the author wrote) as something so powerful. We see it a lot in history too with certain regimes burning books or in instances like the library of Alexandria. It shows the power and truth in knowledge. In this article they mention how it's a form of "censorship" and I think that goes hand in hand with truth and lies.

https://en.wikipedia.org/wiki/Book_burning

Gawain chooses to go to the chapel to confess his sins in part because of his christian values and the chivalric values that he is supposed to uphold. By taking the girdle he is actively participating in a betrayal in both of these ideals. Thus, he feels he needs to be absolved. This may because he is one of Arthur's knights and should not be cowardly or because the lady is another man's wife. However, Gawain still feels the need to confess before he continues.

https://scholarlypublishingcollective.org/psup/chaucer/article/56/2/153/264274/Sir-Gawain-s-Penitential-Development-from

This reminds me of the greek value of xenia. which essentially is "a law/custom of offering protection and hospitality to strangers". It seems to go hand in hand with chivalric values. They both encompass this nobleness that warriors and knights are supposed to represent.

http://www.princeton.edu/~aford/terms.html

Seems almost like what modern satire does. Down to its basics Greek comedies are just another form of social commentary. "Satire in literature is a type of social commentary. Writers use exaggeration, irony, and other devices to poke fun of a particular leader, a social custom or tradition, or any other prevalent social figure or practice that they want to comment on and call into question." The audience isn't supposed to take the story at face value, rather read between the lines.

I think that this elaborates the limitations and faults of the body, of being human. The emphasis on human emotions (jealousy, lust, etc.) is important and essentially the essence of being human. It's also about understanding what that realization means in terms of self. https://www.holybhagavadgita.org/bhagavad-gita-chapter-13/ The nine gates is also a reference to the human body, the gates being the openings to body (mouth, eyes, etc.) "The City of Nine Gates represents the male human body," I think it's also a connection between the body and the chakras as well. http://www.krishna.com/city-nine-gates