There are many major themes in "Sir Gawain and the Green Knight", some more present than others, for instance, honor and pride which lead to manipulation (domination) and finally, the game itself. These are three themes that get the audience interested in the story and give them an appetite for more of the story.
Honor and pride play a big part in the game the Green Knight is playing because it is what he trusts will cause one of the knights to accept his challenge. The knight insults King Arthur and his court deliberately to trigger a response, which he gets. King Arthur is a proud king but this moment in the story is an example of foolish pride on his part. Before he even knew the clauses of the "contract" with the green knight, who stayed vague enough to let him believe that he was seeking a challenge, Arthur says: "Sir courteous knight, if contest you crave, You shall not fail to fight". At this point, the audience wonders why he uses the word "courteous" as an adjective for this insolent knight who burst into the dining room armed, on his horse and asked for "the captain of this crowd". This is the first example of Arthurs foolish pride. He answered this way to save the face of his knights and his court and it will lead him to trouble. The knight exposes the rules of the game and the audience wonders who will take on the challenge, why isnt any of the knight of the round table getting up and accepting the challenge? He goes even further by insulting the king and his court directly, calling them cowards, laughing loud to their face until Arthur blushes, - "The blood for sheer fame shot to his face and pride" - gets up and takes the challenge on himself. Now the crowd is inquisitive. They wonder what will happen to Arthur because surely there is a catch in the knight game and Arthur in foolishly falling into his trap. Now Sir Gawain stands and takes Arthurs place and is asked, by the Green Knight, to swear to seek him out a year from then to complete the second part of the deal . By making this oath right away without hesitation, he shows a great proof of honor and pride. He answers right away: "What is the way there? Where do you dwell?". Of course, now the audience is sitting at the edge of their chair waiting to see if Sir Gawains attack will be effective at all against the Green Knight.
Manipulation and domination and also a major theme in this story because it is what the Green Knight is counting on when convincing King Arthur and his court to accept the challenge. He plays on their pride and honor and knows that they will make their decision based on those two factors, rather that think everything over and make a decision based on logic. The audience likes this because the Green Knight is an appealing "villain". He is huge and proud and not afraid of any of the Knight of the Round Table, and he insults King Arthur to his face, repeatedly from the moment he entered the room. The first manipulative aspect of this knight is the way he presents himself: fearless, proud, arrogant, without armor. "A green horse great and thick; A headstrong steed of might, In broidered bridle quick, Mount matched man aright. This is a form of intimidation and this is the first step in getting Arthur to accept the challenge.