Comments: 8
It's also reminiscent of the shield of Achilles ... presumably?
I dunno; what did the shield of Achilles look like? I bet it didn't have a painting of the Virgin Mary on the inside!
Well, there seems to be some overlap in function of the description, though in the case of Gawain, as I said above, it also serves as the first hint that there is more to the poem than a jolly adventure of yore.
Yes, exactly -- the shield of Achilles was a representation of Ancient Greek civilization, so the message was "this civilization is what we're going into battle to fight for" (as opposed to, "it's just about Helena and we want her back"). Same with Gawain's shield it would seem -- "this is more than a jolly old duel, it's an honest-to-God / Mary quest" ...
Well, the shield itself is saying Gawain gets his courage from his faith but that's not entirely the poet's theme here, I believe. It's just the first indicator that this is going to be a poem about Christianity, just like the previous ones. I'm saving my theory of the whole poem for the eventual review. Right now I'm willing to say that it incorporates but goes beyond the views expressed by Tolkien in the intro to his translation and the similar views expressed by the editors in the intro to this volume.
I'll wait for your review then ... :)

Meanwhile, have you seen this?
https://www.amazon.com/Sir-Gawain-Classical-Tradition-Antecedents/dp/0786420731/
I've not come across it. I was recommended this related work: https://www.goodreads.com/book/show/850129.Sir_Gawain_and_the_Green_Knight
but haven't obtained a copy.

I wonder if the connections to Troy and Aeneas go beyond the introductory stanzas that employ an old legend about the founding of the British nation. Off hand I don't see anything but the most superficial connections to The Odessy. I might pick up this type of thing prior to a re-read.