Defining Shabbat as being “a day of rest” in the conventional sense is not quite accurate. Shabbat is the day that we desist from any kind of creative work. The word for “work” that appears in the Torah is not “avoda” which would mean physical labor, but “melacha” which denotes a different type of “work”.
What is the definition of work? Scientifically it is defined as Force exerted over a Distance (F*D=W). Sociologically it is defined as whatever you do for a living. The Torah, however, has its own definition of work regarding the laws of Shabbat. There are 39 major categories of forbidden activities specified in Tractate Shabbat and the Code of Jewish Law.
The philosophical definition of the type of work forbidden on Shabbat by the Torah is:
a) An act resulting in significant increase in the utility of some object.
b) An act that shows human mastery over the world by a constructive exercise of intelligence. Lifting weights or walking far does not show man's mastery over the world. Physical exertion is not the definition of human work; in most areas of physical exertion animals are superior to us.
"Work" in the Shabbat sense is that act which represents the uniquely human ability to put our intellect to work and shape the environment. The act of closing an electric circuit is therefore more significant on Shabbat than the act of bench-pressing 100K.
We are commanded to acknowledge that our mastery of the world is not absolute, that we have responsibility, and that we have to answer to the true Master of the world, God. True, it is less effort to drive than to walk, however the internal combustion engine, with all its technical wonders and with its thousands of controlled fires and explosion every minute is against both the law and spirit of the Shabbat.