After introducing the Parsha with a broad sweeping imperative "קדושים תהיו," you shall be holy (ויקרא י"ט:ב'), the Torah begins to enumerate many Mitzvos which Rashi (שם בד"ה דבר) characterizes as גופי תורה, essentials of the Torah. The first two of these are the commandments to revere one's parents and to observe the Shabbos (שם פסוק ג). Rashi on this Posuk the well known Halacha which is derived from the juxtaposition of these two commandments that if a parent should instruct a child to violate the Shabbos, the child should ignore that request and comply with the will of Hashem that Shabbos be observed.
It is possible, however, to suggest another reason as to why the Mitzvos of Shabbos and revering one's parents are presented together. The close proximity of the two Mitzvos is in fact not limited to our Parsha. They follow one another in the Aseres HaDibros and the Gemara in Sanhedrin (דף נ"ו.) claims that they were each actually legislated in Marrah, before the people came to Har Sinai. The Midrash states that a person's "פנים," his appearance, during the week is not comparable to his appearance on Shabbos.
Throughout the week, parents are preoccupied with the burden of providing for all of the needs of the family. Suddenly, when Shabbos arrives, the parent is transformed into a person of royalty. The father is a מלך, the mother, a מלכה. Similarly, we find in Pirkei D'Rabbi Eliezer (פרק ל"ט) that אביו של אדם כמלכו, one's father is like one's king. It is therefore on Shabbos when the Mitzvah of educating and training one's children can best be fulfilled. As the mother welcomes the Shabbos, the children notice her becoming the Aishes Chayil about whom it is said פיה פתחה בחכמה ותורת חסד על לשונה, her mouth speaks words of wisdom, and the Torah of kindness is on her tongue (משלי ל"א;כ"ו). It is for this reason that Shabbos is so closely linked with revering one's parents. The day of Shabbos enables a deep bond to develop between parent and child.
Special emphasis on this link is also furnished in the presentation of the Aseres HaDibros. The Halacha states that a parent may not ask a child to violate any prohibition from the Torah. This is derived by the Gemara in Yevamos (דף קי"ד.) from a Posuk (ויקרא י"א;מ"ד) which states that one may not feed forbidden food to one's child; the prohibition is extended to cover all violations. If so, one may ask why it was necessary to emphasize in the Aseres HaDibros "לא תעשה כל מלאכה אתה ובנך ובתך" stressing that not only must one observe Shabbos, but one must also see that his children observe it. Apparently, special considerations ought to be taken to insure a healthy relationship between child and parent that manifests itself most acutely on Shabbos.
This idea in expressed as well in one of the well known Zemiros from Shabbos morning, which states "השומר שבת הבן עם הבת לק-ל ירצו כמנחה על מחבת", the service of one who observes Shabbos together with his children should be accepted by Hashem like a Korban Minchah. Why do we highlight specifically a Korban Minchah when describing the Shemiras Shabbos of a family? The Gemara in Menachos (דף ק"ד:) asks why the Torah, in introducing the laws of the Korban Minchah, uses the expression "ונפש כי תקריב...", "any soul who offers a Korban...." (ויקרא ב;א'). The answer given is that it is the עני, the poverty stricken individual, who is the one generally offering a Korban Minchah and even such a small offering might represent a sizable portion of his earnings. Such personal sacrifice is equated by Hashem to the case of one who is prepared to offer his very soul unto Hashem. The Midrash on Koheles amplifies this and states that Hashem indeed prefers the handful of flour offered by the עני bringing a Korban Minchah to the handful of incense offered by the Kohen Gadol on Yom Kippur. This is the high level of service to which family observance of Shabbos is compared.
We often speak of two categories of people on Shabbos. There are שומרי שבת, those who observe it, and מחללי שבת, those who desecrate it. In reality, though, there is a third category: מבטלי שבת, those who do not desecrate the Shabbos, but simply allow the Shabbos to be wasted and do not take advantage of the opportunity to strengthen the bond between themselves and their children. Hopefully, everyone will cherish this opportunity presented by Hashem's gift of Shabbos so that it will truly be "ביני ובין בני ישראל אות היא לעולם", a permanent sign between Hashem and the Jewish people.