G-d spoke to Moses saying: Speak to the Children of Israel and say to them: G-d's appointed festivals that you are to designate as holy convocations---these are my appointed festivals (Vayikra 23:1)

After this, we would expect the Torah to start listing the festivals. Instead, it says:

For six days, labor may be done, and the seventh is a day of complete rest, a holy convocation, you shall not do any work; it is a Sabbath for G-d in all your dwelling places.

The Sabbath is never categorized as a festival, so why does it appear here at the top of the list? Rashi answers that there is an intrinsic connection between the Sabbath and the festivals. If one profanes the festival, it is as though one profanes the Sabbath; but if one sanctifies the festival, it is as though one sanctifies the Sabbath. How does this work?

Let us take for an example the next festival, coming soon---Shavuot. At Shavuot, we celebrate the Revelation of the Torah to the Jewish Nation. This is intrinsically connected to the Sabbath in the following way: The Sabbath is a day devoted to the fact that G-d created us and the world we live in. But how can we rejoice in the creation of the world if we have no idea what we are here for in the world and how to live in it? Imagine buying the latest state-of-the art gadget. It's so new that you don't even know what it is. Without an instruction manual, you'll be left guessing what it is, and you certainly won't be able to use it.

This is where Shavuot comes in. Shavuot is a day when we celebrate the fact that we received the "instruction manual," telling us what the purpose of this world is and how to live in it. Without it we are lost; so we can't properly rejoice on the Sabbath, either. By celebrating Shavuot we show that the world we live in was created with tremen- dous purpose, and we have the means to fulfill that purpose. This will, in turn, greatly enhance our rejoicing on the Sabbath.