Sir Gawain and the Green Knight has been dubbed "the Rolls Royce of Romances." It was discovered in 1839 and comes from the late 14th century, the time of Chaucer, but from the north of England much removed from the London court, similar to Langland's situation. Claims as to its partaking in the so-called "alliterative revival" are obsolete since it is doubtful that the alliterative tradition ever lapsed.
There is only the one manuscript: Cotton Nero A.x. No references to it exist from the time. The neo-Arthurian nature suggests nationalism; and the garter mention at the end, if it invokes the Order of the Garter, might suggest that this was an occasional poem.
Potentially useful questions to focus the reading:
Campbell, Joseph, with Bill Moyers. The Power of Myth. NY: Doubleday, 1988. 152-153.
Pearl, Cleanness, Patience, Sir Gawain and the Green Knight. Ed. A.C. Cawley and J.J. Anderson. NY: E.P. Dutton and Co. Inc., 1976. ISBN 0 460 11346 1.
Sir Gawain and the Green Knight. Trans. Marie Borroff. NY: W.W. Norton & Co., 1967. ISBN 0-393-09754-4.
Sir Gawain and the Green Knight. Ed. James Winny. Lewiston, NY: Broadview Press, 1992. ISBN 0-921149-92-1.