Sir Gawain and the Green Knight

Last night I went to see The Village Quire perform little known carols with readings, and I was delighted to find that one of the readings was the first appearance of the Green Knight at the Court of King Arthur, from the medieval poem Sir Gawain and the Green Knight.
The Village Quire sing a capella part songs, and some of the Christmas ones, like Gaudete and the Boar's Head Carol, go back to the Middle Ages.
Sir Gawain is also medieval. The only copy that survives was written down in 1400, in the dialect of the north-west midlands, in alliterative verse. The anonymous writer was familiar with aristocratic life, which is described in detail, and one theory is that he was part of John of Gaunt's court. In the portions of the poem where Gawain is searching for the Green Chapel, to meet the Green Knight again and fulfil his part of the bargain they struck, the descriptions match North Wales and the Wirral. That may be one reason it's one of my favourite medieval poems - the Welsh and North Western links - and the story is great fun, too.
It's one of my traditions of Christmas to listen to an old cassette tape of Ian McKellan narrating the story on a long ago Radio 4 programme. This was long before he ever became Gandalf, or even Sir Ian.
As you'd expect for a half hour programme, they had to leave a lot out. One passage describes Gawain being armed before he sets out, and goes to some lengths to explain the strange device on his shield, which to modern eyes seems quite unsuited to a Christian knight.

"Then thay* shewed hym the schelde, that was of schyr goulez,
Wyth the pentangel depaynt of pure golde hwez"

"Then they displayed for him the shield, which was of bright gules with the pentangle picked out in the colour of pure gold. He seized the shield by the baldrick and slung it about his neck; it suited the knight fittingly and well. And just why the pentangle is appropriate to that noble lord I am bent on telling you, even though it should delay me: it is a symbol that Solomon devised once upon a time as a token of fidelity, appropriately, for it is a figure which contains five points, and each line overlaps and interlocks with another, and it is unbroken anywhere,; and all over England, so I hear, it is called the endless knot. And so it is appropriate to this knight and to his unblemished arms; because he was always trustworthy in five respects and fivefold in each, Gawain was known to be a good knight, and like refined gold, free from every imperfection, graced with chivalric virtues...."

And it goes on to talk about the five senses, the five fingers, the five wounds of Christ, the five joys of the Queen of Heaven and his five virtues.

(from WRJ Barron's translation and notes)

*(the 'th' sounds above should be shown by the letter 'thorn', a medieval letter which has fallen out of use)