Geoffrey Hill, in festive mood. Although I think I can get the gist of the poem, I frankly have no idea what it’s got to do with Christmas trees. The inverted commas around the title are Hill’s, and perhaps provide some clue. Answers on a postcard …
“Christmas Trees”
Bonhoeffer in his skylit cell
bleached by the flares’ candescent fall,
pacing out his own citadel,
restores the broken themes of praise,
encourages our borrowed days,
by logic of his sacrifice.
Against wild reasons of the state
his words are quiet but not too quiet.
We hear too late or not too late.
(Haven’t bought ours yet, by the way. Hope it’s not .. er … too late.)
Caspar David Friedrich : Winter Landscape
The Crimson Rambler 
Nope – no idea at all.
I have now got a tree, at least. Perhaps if I stare at it for long enough the answer will come to me.
I believe “Christmas Trees” were the name given by the Germans to the parachute flares used by allied bombers to light the target zones (“the flares’ candescent fall”). These light B in his cell at Tegel, illuminating a revived nativity.
Thanks very much. Makes perfect sense. Illuminating.