İt is about middle English. Actually, it emphasizes manners of knights towards to their kings . And , here there is a monster who is green knight because his colour , clothes and even his horse are green. This symbolizes nature. İn this time, nature is both natural and wilderness. So , he also has evilness. Sır Gawain uses a girdle to product him. That's why, this is a trick and it is against the chivalric manners. Green knight actually tested their manner here. İt is also a type of shame for knights. Moreover, the game which they played is important.