“However, you must observe my Shabbos, for it is a sign between Me and you for your generations, to know that I am Hashem, Who makes you holy.” (Shemot 31:13)
The Pasuk states that Shabbat is a sign between us and G-d. What does it mean that Shabbat is a "sign"?
Imagine that it's been a long day and you barely ate anything. You hop over to the pizza shop and the lights are off - the store is closed. "Interesting," you think to yourself, "they are never closed at this time." A few days later you pass by in the morning and again it's closed. You figure that the owner must be away on vacation. A week later it's still closed. You assume that they must be renovating. One day you pass by and you see that the sign "Delicious Pizza" has been removed. You now understand that the store has closed down. Once the sign is removed you know it no longer exists.
Shabbat is the cornerstone of our faith and is equivalent to all of the commandments, for through the commandment of Shabbos one expresses his belief that G-d created the world in six days and rested on the seventh. Observing Shabbat indicates that one believes in the Creator. When one desecrates Shabbat he's removing his sign of being a believing Jew.
Shabbat helps us understand our place in the world. During the week human beings are busy building and changing the world. Every seven days we stop, we pull back from building the world and remind ourselves that we are not G-d. In ceasing from all creative activity we make the statement to ourselves and to humanity that although we can manipulate the world, we don't own it; the universe belongs to G-d.
Shabbat is not a day of restrictions; it's a day of opportunity. It's a day you can sit back knowing that you're in G-d's hands and that everything is being taken care of for you. It's a day that enables you to refresh, reconnect and rejuvenate.