Children’s stories often reveal deep truths. Dr. Seuss especially had a habit of hiding important lessons in cute children’s books. The Lorax is clearly a pro-environmentalist book. Its lesson is that we should not take things for granted. Specifically, it is everyone’s responsibility to preserve the environment. Complacency results in destruction of what we take for granted, such as trees.
The book was controversial as soon as it was published in 1977, and as you can see from the movie, it still is! For me, the book has been a reminder that the environment is fragile, and that the interests of those making money should not take precedence over the needs of the rest of us. Some things, once they are lost, cannot be regained.