Passover, now upon us, apart from being an occasion for family reunions and indigestion, is the right time for a more serious activity:

I mean, reflecting on the claim that our religion is highly rational and even the claim that Judaism is "true." Far from being ethnic chest thumping, this assertion of truth can be defended with a straight face.

I realize I'm inviting controversy, not least among Jews. We live in a funny world, as I'm frequently reminded when speaking to audiences at bookstores and synagogues about my book, "Why the Jews Rejected Jesus." The book addresses Christian proofs of the Christian faith, and yet it's often Jews who bristle at being told their religion is true. At one large suburban Conservative temple where I spoke, the organizers brought on a professor from the Judaic studies department at the local university to dispute me.

But before we get to truth, let's discuss rationality. What makes Judaism rational is the reality that Passover, the most widely celebrated of all Jewish festivals, is incomplete without the holiday that follows 50 days later, Shavuot, one of the least celebrated or observed by American Jews. Passover recalls the Exodus from Egypt. Shavuot commemorates the revelation of the Torah to Moses and Israel at Mount Sinai. Without Shavuot, Passover would be meaningless.

The reason has to do with whether the principles of Judaism are to be believed because of long-ago miracles. The Passover story of liberation from pharaoh's slavery, told in the Haggadah, is studded with miracles. There are the 10 plagues, called down by Moses, which devastated Egypt while leaving the Jews unscathed. There is the crossing of the Sea of Reeds, which Moses parted, allowing the Jews to pass between walls of water - which then drowned the Egyptian army that tried to follow.

Nice miracles!

Yet in Maimonides' epic-length distillation of Jewish oral and written tradition, the Mishneh Torah, that arch-rationalist sage explains that the people "Israel did not believe in Moses our teacher because of the signs he performed, for he who believes because of signs is subject to doubts in his heart."

Only at Mount Sinai, where the escaped slaves personally encountered God and heard His voice for themselves, did they come to believe as Jews.

In the story of Shavuot, no miracles figured in the Jews' acceptance of the Five Books of Moses. And were it not for Sinai and Shavuot, the newly freed Jews would have wandered off, disappeared into anonymous history, never becoming the eternal Israel.

Only at Mount Sinai, where the escaped slaves personally encountered God and heard His voice for themselves, did they come to believe as Jews. It was that personal experience of God that created the Jewish people - not any miracles, however impressive, conjured through a human being. To reinforce that connection, each generation of Jews serves as a witness to every subsequent generation in an uninterrupted succession down to today.

Had that unbroken chain passed down only the testimony that signs and wonders happened, those wonders could be dismissed as sorcerers' tricks or natural occurrences. There is a radical difference between hearing God speak the Ten Commandments, on one hand, and seeing a human being apparently split a sea, on the other. Someone who believes the main claim of Judaism - that God gave the Torah to Moses - does so on the basis of eyewitness testimony regarding the main claim, a more rational standard of belief than testimony about miracles.

So Maimondies teaches. And based on the Bible's narrative, he makes a strong case. At Sinai, God told Moses, "Behold! I come to you in the thickness of the cloud, so that the people will hear as I speak to you, and they will also believe in you forever" (Exodus 19:9).

From then on, future prophets who followed in Moses' footsteps were to be accepted not simply on the basis of miracles they might perform. Though miracles were one criterion for establishing a true prophet, the main factor was faithfully upholding Moses' prophecy, the Torah.

Future miracles only mattered in establishing new prophets because Moses said they did (Deuteronomy 18:15-22). The experience of Sinai, through which the Jews came to believe in Moses as God's spokesman, serves as the guarantee of future prophetic authenticity. Maimonides writes, "If there arises a 'prophet' who performs miracles and wonders but seeks to deny the prophecy of Moses our teacher, we need not listen to him." Indeed, such a person is to be executed (Deutronomy 18:20).

Jesus comes to mind - a man whose claim to authority is based on miracles - from feeding the multitudes with a few loaves and fish to reportedly being resurrected. And by dint of these miracles, he and his followers dispensed Jews from following Moses' Torah.

The odd thing is, when I explain such matters to groups of mixed Jews and Christians, even as the Jews grumble, it's the Christians who are uniformly encouraging and cheerful about a Jew asserting the truth of his faith, even when that assertion contradicts their Christianity. At Passover and year-round, it is, as I say, a funny world. n

This article originally appeared in The Jewish Journal.