The mitzvah of honoring one's parents was given in the desert, where the Jews did not have to rely on their parents for food or clothing. This is to teach that honoring one's parents is due first to the fact that a person's parents brought them into existence and only after that are all the details of the parents giving to the child added.
Honoring parents is a lesson for honoring G-d. First a person should acknowledge that his entire existence comes from G-d. Then he should add all the other great gifts that G-d has given him to the list of things to appreciate.

- Adapted from a sheva brochos speech by Nasanel Lerman