From wiki:

The story is commonly recognized as a fable concerning the danger of greed causing human destruction of the natural environment, using the literary element of personification to create relatable characters for industry (the Once-ler), the environment (the Truffula trees) and environmental activism (the Lorax). The story encourages activism and involvement in making the situation better: a quote from the Lorax states, "Unless someone like you cares a whole awful lot, nothing is going to get better. It's not".

Dr. Seuss singled out The Lorax as his personal favorite of his books – in it, he managed to create an engaging story highlighting how economic growth is often prioritised over environmental issues. Dr. Seuss stated: "The Lorax came out of me being angry. The ecology books I'd read were dull...In The Lorax I was out to attack what I think are evil things and let the chips fall where they might".