What are some purposes of the poem Sir Gawain and the Green Knight?

The famous medieval poem Sir Gawain and the
Green Knight seems to have a number of related purposes, including the
following:

• To remind its readers that earthly
  life is mutable – that nothing earthly will last or can be depended upon (see lines
  16-19 of the Marie Boroff translation).


• To remind its
  readers that the true meaning of Christmas does not involve self-indulgent celebration
  but rather genuine religious thankfulness for the birth of the savior
  (20-84).


• To rebuke the pride and immaturity of King
  Arthur and his courtiers as they are described in the opening section of the
  poem.


• To remind us of the moral and religious virtues to
  which we should all be dedicated (at least according to the author of this poem;
  619-69).


• To contrast the shallow life Gawain was leading
  during the first Christmas described in the poem with the true meaning of Christmas,
  which becomes apparent to him a year later (750-62).


• To
  show us how easy it is to forget spiritual lessons, even when they have been learned
  through recent and difficult experience (875-900).


• To
  show us how tempting earthly, physical pleasures can be
  (875-900).


• To remind us that physical beauty may have
  nothing at all to do with spiritual beauty (941-69; 1236-40; 1472-1475;
  1531-34).


• To show us that even a man as good as Gawain is
  capable of succumbing to temptation (1859-69).


• To show us
  that even a man as good as Gawain is capable of lying
  (1940-41).


• To show us that even a man as good as Gawain
  is capable of hypocrisy (2138-39; 2156-59).


• To show us
  that forgiveness is a great Christian virtue
  (2389-94).


• To show us that self-forgiveness is also a
  worthy thing – that we should not expect perfection from ourselves or others, since we
  are all imperfect (2505-10).


• To show us that Gawain is
  wrong when he proclaims, concerning his own faults,
  that

readability="10">

“ . . . one may keep a deed dark, but undo it no
whit,

For where a fault is made fast, it is fixed
evermore.”
(2512-13)

• To
  remind us that the whole point of the birth of Christ and of the Christian religion is
  precisely that faults can be forgiven and that sins need not be
  “fixed evermore.”


• To show us how much more mature and
  truly Christian Arthur and his court have become by the end of the poem than they were
  at the beginning. Their decision not simply to forgive Gawain but to embrace him in love
  reveals that they are truly practicing the religion to which they earlier gave mere lip
  service (2513-21).