The holiday of Shavuot is a mystery to many of us, and not just because most kids are on summer vacation during Shavuot, so the holiday is not covered in school.
The date is that of when we received the “Ten Commandments” (more accurately translated as the “Ten Statements”) from G-d; not on the tablets, but rather hearing them. Sort of. We actually only heard the first two statements, after which we were so frightened we requested that the rest go through Moses, to be transmitted to us. And according to tradition, we died in between each statement (is this the origin of the phrase “I was scared to death”? I don’t know!
For this reason, on Shavuot we read the part of the Torah describing this event. We stand at attention, reliving the receiving of the Torah.
Wait… Torah? Didn’t we just say G-d uttered the Ten Statements? So… why do we describe it as “The time of Receipt of the Torah?”
This is my understanding, based on my discussion last week with Rabbi Mandel (Fort Worth Chabad). I hope I got this right: The “Torah” is both the pentatuch, and the law. On Shavuot, we received all of the law, being the 613 commandments (the meaning of “Mitzvot”), and we accepted the obligation to fulfill them. The first Statement, “I am the L-rd your G-d who brought you out of the land of Egypt, the house of bondage” was a positive one, which encompassed all 365 positive commandments (the “thou shalt” ones, 365, because every day we have to do what G-d wants and also we traditionally are said to have 365 sinews in our body). The second Statement, “You shall have no other gods besides Me,” being a prohibition, encompassed all 248 negative commandments (the “thou shalt not” ones , 248 being the traditional understanding of the number of organs and limbs in our body, because every part of us must refrain from doing that which G-d wants us NOT to do).
So in this context, we receive all of the LAW, being the Torah, on Shavuot.