The foundation of Judaism is that man and the universe have a purpose, because they were created by a purposeful being called G-d. One of the main things we can say about G-d is that He is good, and He loves and is deeply connected to everything in creation.
Since G-d is absolute perfection, He has no needs and did not need to create the world. We are taught that He created the universe to bestow good upon man. The greatest good that can be bestowed is giving each person the ability to become G-d-like and thereby connected to G-d for all eternity. The mechanism to become G-d-like is by learning and observing the mitzvos in the Torah.
Observing the mitzvos is not easy because we are composed of two opposites—a pure spiritual soul and an unenlightened physical body, which are in a constant state of battle. Since we all have different natures and different life circumstances, we all face different spiritual battles that change as we grow. The Torah gives each of us the exact prescription we need to be successful in our battles at every moment of our lives.
Shavuos is the day that Hashem gave the Torah to all of the Jewish people, meaning that every person experienced an absolutely clear revelation of G-d through the transmission of the Torah. The Torah that was transmitted that day was the Ten Commandments, which are the ten categories under which every mitzvah falls.
The spiritual power of Shavuos, and indeed every Jewish holiday, is available on the day of the holiday every year. On Shavuos, we can tap into the power of internalizing our purpose of becoming more G-d-like through the learning of Torah and the performance of mitzvos. Since we each have different natures and life experiences, we each have a unique opportunity to actualize our potential and purpose.
A truly awesome day. Have a good Yom Tov.