First let's start with a fact everybody agrees upon: There exists today a group of people, the Jews, who claim the following: "3,300 years ago, millions of our ancestors experienced what they felt was G-d talking to them. We, their descendants, have an unbroken chain passed on through the millennia that tells us two things: (1) That the event took place, and (2) The contents of the message." The Jews are the only people to ever make such a claim.
Let's first look at point number one.
How can you explain a group of people who claim to be descendants of millions of people experiencing the splitting of the sea, the manna and the Revelation at Sinai? How did the first generation start believing it? A charismatic leader? A slowly evolving story? Mass hypnosis?
Could a leader rewrite the oral history of a people and get them to believe it happened to their own ancestors? Imagine Napoleon telling the French "In the year 750, God split the Rhine River for your ancestors, commanded them a set of all-encompassing laws, and they passed that experience down from generation to generation." The people would say "What? Dad never told us that! Hey, Grandma, did your grandparents ever tell you about this?" Remember: We not only believe in the Exodus and Sinai, we also believe that we have an unbroken chain back to those events.
Or the slowly evolving story: The people ate sap from bushes that grew in the desert, but used to say "God sent us food from heaven" because they wanted to express the idea that all nature comes from 'Above.' One day, Johnny comes home from kindergarten and says, "Dad, the teacher told us that food fell from the sky." The father, reading a newspaper, grunts "Uh huh," and Johnny grows up with a misconception. Eventually, Johnny's misconception becomes the predominant belief. Slightly absurd. And what about Sinai? Was it really a volcano that 'grew' to become a mass prophecy of 613 commandments that we all agree upon?
Mass hypnosis? Martians? Now we come to a second problem. No matter what theory you concoct to imagine how such a belief got started, you must answer the following question: Why are we the only ones in history ever to make such a claim? Why, indeed, didn't Napoleon create such a belief? Why didn't Pharaoh or Hammurabi, Paul or Mohammed, Alexander or Julius, Lenin or Mao? They all could have 'propheted' greatly. No people, clan or country across the globe at any time in recorded history ever claimed that God convened their nation and spoke to them. Except us. Why?
Is it that the Jews were simply the most ignorant, superstitious, stupid and gullible people ever to walk the face of the earth? But then, having accepted this belief, they became the most scholarly, unyielding, skeptical people in the world, earning the title 'People of the Book,' surviving the ideological onslaughts of Christianity and Islam, giving their lives to pass on this belief, becoming a 'light to the nations' and spreading morality and monotheism to all humanity?
The Torah itself predicts that no one else in history will ever make a similar claim: "Inquire into the earliest days, the past, from the day God created people on the earth, and from one end of the universe to the other: Was there ever such a great thing as this, or was there ever even heard a claim like it? Did a nation ever hear the voice of God speaking from the midst of the fire as you heard, and live (to tell about it)? Or did God ever attempt to come and take a nation out from the midst of another nation with miracles, signs, wonders, and with open expressions of Divine might, and with great awe, like all that the Lord your God did for you in Egypt in front of your eyes?" (Deuteronomy 4:32-34)
Now, how do we know the events and laws were transmitted faithfully? Well, we see Jewish communities dispersed across the globe for
