"Every man must revere his mother and father." (Vayikra 19:3)
In addition to the mitzvah to honor our parents, we are also commanded to
revere them, which includes not to stand or sit in their designated places
and not to interrupt or contradict them. The Rambam teaches that we are
to act toward our parents as if we are afraid that they might punish us,
as a king would punish his subjects (Sefer HaMitzvos, mitzvah 211).
We fear our parents because the are the agents of Hashem who brought us
into the world.
The Torah places this instruction in Parashas Kedoshim right after the
command, "You shall be holy" (Vayikra 19:2). We see from this that
revering our parents is the first step toward the ideal of holiness and
perfection. Fearing our parents will cause their teachings of Hashem's
Torah to be more effective. Developing our awe and obedience toward our
parents will help us develop that attitude toward Hashem as well.
When one of the Sages in the Gemara heard his mother's footsteps
approaching, he said, "The Shechina is coming" (Kiddushin 31b).
One may not obey his parents if they request something that is against the
Torah's commands (Sefer HaChinuch, mitzvah 33).