The Revelation at Mount Sinai is clearly the greatest day in human history. This was the day when the few million Jews actually heard G-d speak.
This also represented the beginning of the Jewish people, in their fulfillment of their unique role in the world. They were to teach and set the example of all that was right and moral in the world. They were receiving the Torah directly from G-d.
No religion in human history ever began in such an outward manner. There could be no doubt as to the truth of Judaism, as there was no doubt that they were hearing the word of Hashem, directly from Him.
It is critical for all Jews to accept the concept of “Torah from Sinai,” and believe that this event actually took place. We are also to reinforce the idea that both the Written and Oral Law were given on that incredible day.
If we accept this, we also accept the Divine aspect of our religion. All of our laws that were handed down from generation to generation, have a Divine stamp connected to them. We follow its dictates, because we believe that this is the fulfillment of G-d’s will.
Those who do not believe accept that this great event happened, turn Judaism into a man made religion, rather than G-d given. We must remember that all began at Sinai!