Then sudden Felagund there swaying
Sang in answer a song of staying,
Resisting, battling against power,
Of secrets kept, strength like a tower,
And trust unbroken, freedom, escape;
Of changing and of shifting shape,
Of snares eluded, broken traps,
The prison opening, the chain that snaps.
The metaphor is so obvious. Easter Island isolated in the Pacific Ocean - once the island got into trouble, there was no way they could get free. There was no other people from whom they could get help. In the same way that we on Planet Earth, if we ruin our own [world], we won't be able to get help.
Yet there are moments when the walls of the mind grow thin; when nothing is unabsorbed, and I could fancy that we might blow so vast a bubble that the sun might set and rise in it and we might take the blue of midday and the black of midnight and be cast off and escape from here and now.