Penny I interpret it as a message to humankind to be still and see things from the timescale of trees and a larger perspective. It is a central theme of the book that we are not able to perceive slow and long changes, which has led us to do massive harm to trees, our planet, and ourselves.
Skye Michel I think Nick is encouraging a slowing down of human speed/lifestyle as the ultimate way to save ourselves and surrounding lifeforms. I think back to Neelay's favorite sci-fi story about humans moving so slowly that they're perceived by aliens as unintelligent blocks of meat to harvest. Later in the book (near the section where Nicks STILL artwork is described) the sci-fi story is connected to our human inability to recognize tree intelligence (due to their slow nature) and our subsequent harvesting of their meat. While Neelay's storyline could be an offer of hope as his "learners" are trying to discover all they can to save humanity, the learners are also guilty of working at a faster-than-human pace. Juxtaposed beside Nick's last message, the success of the "learners" in saving humanity/the world is undermined by the rapidness of their efforts (aka saving the world/trees may not come from faster technology). There is also a hinting that humans will be undermined by the growing intelligence of the "learners" they've created, making Neelays favorite sci-fi story a repeating theme for evolution / life (quicker lifeforms evolving from slower ones and contributing to their ancestor's demise). Thus Nick's message of stillness is a plea to change our pace and a challenge to the repeating outcome of Neelay's favorite sci fi story. In slowing down / being still we can open ourselves up to the intelligence of life forces we otherwise wouldn't recognize, saving both surrounding lifeforms and ourselves.