Sir Gawain

The main question that I have from Sir Gawain is what is the point of the beheading or attempted beheading? I get that the game the green night wanted to play was dangerous and showed courage in whichever man was brave enough to play. However, after the green knight was beheaded he simply picked up his head and one year later when the green knight tried to cut off Sir Gawain's head, he was only able to make a small cut on the back of his neck. So my question is what was the purpose of decapitation here? Was it supposed to symbolize something else important? And if so, why were none of them successful ( I recognize that the green knight's head is successfully cut off but what is the point if he is able to simply pick his head up and move on with his life?

I commented on Brax's and Sierra's!