Leviticus 19:3 Ye shall fear every man his mother, and his father, and keep my sabbaths: I am the LORD your God.
The command to honor our parents is the only one of the Ten Commandments to be accompanied by a promise. This command to fear them as well is associated with the Sabbaths in part because both are given for our own benefit. We are not to keep the various Sabbaths for God, but for ourselves.
God gains nothing tangible by the honor and fear we give our parents, while we gain longer and happier life through obedience and learned wisdom.
Mothers are given precedence because we do not naturally fear them. (I suppose that greatly depends on your mother!) In most circumstances, it is easier for a child to fear his father. He is threatening and powerful, while mothers are kind and comforting. Yet God says that we are to treat our mothers with fear for our own profit in spite of our natural inclination.
