While I do not believe in anything myself, I think I can help with this. The environment or world was created by God in the bible. Therefore, respecting the world and taking care of it could be seen as a physical representation as a devotion to God himself. It would considered the same as respecting other people in the eyes of God. If you had created something for someone, you would want them to protect it, would you not? This world is the reason you are able to live your life devoted to God, so I could see why it would be important to protect. There may be another (more spiritual) reason, but this is what I thought of when reading your question.
