You shall honor it [Shabbos] by refraining from your usual weekday practices, nor pursuing your business, nor speaking thereof (Isaiah 58:13).
The observance of Shabbos and the festivals is characterized by not only abstinence from work, but also from all types of "weekday" activities, including even how one converses. "Your conversation on Shabbos should not be similar to your weekday conversation" (Shabbos 113b).
A personal incident illustrates that by properly honoring the Shabbos and festivals, one achieves the respect of others.
As a resident in psychiatric training, I explained to the program director that I was unable to work on the festival days, and that these should be considered vacation days and deducted from my allotted vacation time.
The director shook his head. "No need for that," he said. "Non-Jewish people can do anything they wish on their holidays. If they can wash the car, paint the garage, or go to the theater, then they can just as well come to work. In your case, you are not permitted to do anything, so obviously you cannot come to work, and this need not affect your vacation time."
It has been said, "Even more than Israel has kept the Shabbos, the Shabbos has kept Israel." If we honor the Shabbos properly, the Shabbos will honor us.