Theme Of Chivalry In Sir Gawain

What is chivalry, exactly, and how does Gawain demonstrate the chivalric ethos in the first two sections of the poem? [ ethos= ethical philosophy]
Chivalry is the sum of the ideal qualifications of a knight including courtesy, generosity, valor, and dexterity in arms. The way Gawain demonstrates chivalric ethos is that he honors the King and shows bravery and humility by accepting the Christmas challenge and not allowing the king to do so. He keeps his word by going to the Green Chapel on the day agreed. He keeps his word by giving the Lord the kisses he gets from his wife. He respectfully refuses the advances of the Lord's wife showing loyalty and respect for ladies. He owns up to his mistake, confesses, and apologizes.
Why is Gawain

The Green Knight applauded Sir Gawain for living up to his end of the bargain. The Green Knight swung twice at Gawain’s neck and the first time Gawain flinched and the second time the Green Knight stopped right before his neck. The third time the Green Knight swings the axe and breaks the skin but doesn't decapitate Gawain. Which led to the Green Knight explaining to Gawain that he is actually the same lord of the castle where Gawain spent his holidays. The first two blows, he claims, were in return for the way Gawain returned the kisses of his wife, following the rules of their game as an honest man should. The third blow, he says, was for Gawain’s failure to return the green girdle to him on the last day. But because Gawain’s failing was only because he wanted to save his life, and not because he's just dishonorable, the Green Knight forgives him. He leaves Gawain with only a scar and a girdle as a reminder of his very human sin. Gawain returns to King Arthur’s court all ashamed and sad that he’s failed a test of honor by withholding the green girdle from Sir Bertilak out of a desire to preserve his own life. He feels like he’s failed in his duty as a knight and let everyone down. Perhaps, more importantly, he’s learned that he’s not perfect and never will be. He explains to the whole court that he plans to wear the girdle forever as a reminder of his failing, because "a man may hide his misdeed, but never erase it, for where once it takes root the stain can never be lifted". But instead of being properly sobered, the whole court laughs at Gawain’s words and agrees that everyone in court will wear a similar girdle for Gawain’s