If not -- what's it all about?
While it is true that the momentous revelation at Har Sinai was on Shavuos, the complete Torah as we know it was actually transmitted to Bnei Yisroel over time, in bits and pieces, throughout their travels in the desert. Even the original Luchos, which were given to Moshe at Har Sinai, were broken and replaced.
With that in mind, Rav Chaim Friedlander zt”l asks in his classic sefer, Sifsei Chaim, why do we celebrate Shavuos as the day of Matan Torah, the giving of the Torah? We would understand the day if it were the commemoration of Hashem’s revealing Himself to us. Or even of our national, united accepting of the Torah. But to commemorate the giving of the Torah on Shavuos seems to, at best, completely miss the boat!
Rav Chaim answers based on the words of Ramchal in his work, Daas Tevunos. Ramchal explains that at Har Sinai, Hashem gave us the power to spiritually affect the world. Even with our own preparedness to serve Hashem, we could not properly achieve this without the G-d-given ability to tap into spirituality. Through the giving of the Torah by Sinai, Hashem put the power of the Torah in our hands. Now, through the Mitzvos, and primarily limud haTorah, we bring the world towards perfection. On Shavuos, we commemorate the giving of this awesome ability.
May we be zoche to properly celebrate the Yom Tov and renew our appreciation for the tools we have been given.
Good Yom Tov!