The number three is very important in the prose work "Sir Gawain and the Green Knight".
The first time the number three appears in the text as Gawain is leaving Arthur's castle to keep his promise to the Green Knight. Gawain crosses himself three times and asks Christ to give him speed.
The second appearance of the number three appears when Gawain is speaking of how long he has been traveling to find the chapel of the Green Knight.
In the third appearance of the number three, Sir Gawain has arrived at Lord Bertalik's castle and they have made a promise to each other to give to each whatever they receive during the day. The trumpets blow three times signalling the beginning of the first day's hunt.
The fourth appearance of the number three comes, again, during another hunt day. Three of Bertalik's men throw themselves onto a boar to submit him. The boar is too strong and the men fail.
The fifth reference to the number three, again, is during another hunt. This time Bertalik and his men are pursuing a fox. The reference to three is that the fox was being threatened "threefold" by the men and elements around him.
The sixth and seventh references to the number three is spoken of when Lady Bertalik gives Gawain three kisses and Gawain, then in turn, gives the three kisses to Lord Bertalik.
Overall, the number three is used, as was typical in Medieval literature, to provide symmetry to the text. The collections of threes which exist are also important:
-Lady Bertalik goes to see Gawain on three separate occasions.
-Lord Bertalik goes hunting on three seperate days.
-Lady Bertalik kisses Gawain three seperate times.
-Gawain swings the axe upon the Green Knight three times.