Why do we eat dairy on Shavuot?
When G-D created the universe his first command was: "Let there be Light!"
This of course was not a physical light since the physical light was created on the fourth day in the form of the Sun, the Moon and the Stars. The first day's Light was the spiritual Light, the manifestation of G-D-liness on earth. This Divine Light was necessary in order to create a creature in G-D's image, a human being, in a mundane world. Just like a painter proudly puts his signature on a masterpiece, G-D has put his "signature" in our world, his proud creation, in the form of a Divine Light.
Our soul, G-D's "signature" inside of us, our Divine essence, always wants to ascend back to be with the Creator. In order to ease our soul's yearning to reunite with the Creator, G-D decided to send another Divine instrument into the earth so our soul would not be so lonely in our physical world.
This is where the Torah comes in. Since the Torah is the word of G-D as was taught to Moses on Mt. Sinai, it too is Divine and acts as a "Mate" to our own soul.
This is why the holiday of Shavuot, the time of "sending" the Torah to earth is so important. It is the time when G-D made sure that our spiritual essence will have a counterpart so it could be content here on Earth, thus allowing it to develop and flourish.
For the Jewish people, the nation which was assigned to be the keepers and guardians of the Torah, this merging with our souls was relatively fast. Yes, there were issues with our ancient forefathers who strayed away from the Torah but our biblical prophets always kept us in line - some through much effort. For some other nations however the merging process is still ongoing...
So what is this "Merging" all about? The words of the Torah resonate well with us. They awaken our Divine Essence and cause us to be more than physical beings walking on this earth. Cantor Lee and I experience this and observe it with others every time the Torah is read in public.
This is true of our Bar/Bat Mitzvah students who begin to mature after the experience of chanting from the Torah in front of their families. This is true of chanting during our Friday night services or during our spiritually charged Shabbat circle services, when a special "electricity" is created among us.
The holiday of Shavuot is therefore spiritually unique and dear to our heart. While the holiday of Passover denotes the time when we became a nation, the holiday of Shavuot honors the time when we became Jews and the time when mankind received its spiritual dimension to support and complete its physical existence.
And about that dairy question:
After receiving the Torah, including the dairy laws, our ancestors realized that they could not eat the already prepared meat dishes since it was not done in accordance with the newly given dietary laws. Until they could prepare new meat dishes they probably ate blintzes, cheesecake from the Cheesecake factory, lox and bagels, white fish on a bagel with cream cheese. (The cardiologists among the Israelites needed to make a living too didn't they?)
(Here is Cantor Lee's post about Shavuot from a few years ago: Healing Light of the Torah )
May we all experience the Light of the Torah!