The Arctic Incident Code
The Code

Image from www.eoincolfer.com, but I have taken out some of the grid lines, to make it easier on the eye.
Decoded
“Congratulations Human. If you have cracked this code then you are more intelligent than most of your species. This is a message from the Fairy People.
We are seeking out our allies among the Mud Men. Though most Humans are dullwitted creatures there are exceptions. You for example. The reason for your intelligence is that you have Fairy ancestors. Do you feel different from those around you? Are your ears a bit pointier than most is your tongue long enough to touch your nose? Do you dream of flying? Have you ever thought that you do not belong among the Mud Men? That is because you have Fairy blood in your veins.
So young Mud Fairy I have a mission for you. As one of the People it is your duty to protect the Earth from those who would destroy it. You must become one of a new race of Mud men who love this planet as much as the Fairy Folk. There is one simple rule. Use only what you need and use it wisely. Do this and the Earth will survive. Go now and begin your quest. I shall repeat this message for those Humans whose Fairy intelligence is buried a bit deeper than yours.”
The explanation here is pretty simple. Be an environmentalist. This kind of speech is the sort of thing 'Greenpeace' and other environmentalist groups would be proud of. Take care of the environment. It won't last long otherwise... Well, that, and the books thinks we are smart! Yay!
The message then repeats itself throughout the rest of the book.