What great day? Why, the Feast of the Transfiguration, in case you didn't know! (S'OK, per usual I did not either, until noon Mass.)
One cannot let these things go by unmarked. And so:
We shall all be changed ...
Of note: While the video was uploaded only a couple years ago, something in the ladies' ensembles is screaming "1970s" at me. Still, it's nice that they didn't require concert blacks all the time.