Rambam - Sefer HaMitzvos: Negative Mitzvah 321: Negative Mitzvah 321

Negative Mitzvah 321: It is forbidden to go beyond the permitted distance from a city on Shabbat
Exodus 16:29 "Let no man go out of his place on the seventh day"

HaShem gave us the holy day of Shabbat.

He wants us to rest, be peaceful and concentrate on using this special day in a meaningful way.

Many of the laws of keeping Shabbat help us in creating this peaceful atmosphere and feeling of holiness.

We usually feel much more relaxed and calm when we stay in our own home and surroundings.

We are prohibited to journey, even by foot, a distance that is over 2000 cubits (approximately a kilometer) from the edge of town on Shabbat.

Within the settled area of a town or city, there are no limits on the distance we may walk on Shabbat.

When G-d makes a miracle, it is so that afterwards we may look at the natural order of things and say, "I recognize this. This is not what it appears to be. This, too, is a miracle."

From: Bringing Heaven Down to Earth by Tzvi Freeman - tzvif@aol.com