Why was the judaic revelation so important?

Answer 1

The revelation of the Tanakh (Hebrew Bible) is important because it tells the history of the ancient Israelites, as well as giving us the teachings of such prophets as Moses, Isaiah and Jeremiah, the stories of kings like David and Saul, and the development of the ethics and beliefs of the Jewish religion. Our tradition is that the Hebrew Bible is from God (Exodus 24:12), given to us to provide knowledge, guidance, inspiration, awe and reverence, advice, law, comfort, history and more. It is the basis of Judaism. It crystallized, strengthened and codified our beliefs; insured our awareness and knowledge of our identity and history; and provided powerful impetus to be ethical.
It made us stand in awe of God, while also providing optimism and comfort through the prophecies of redemption. It inspired us to strive for holiness and informed us how to pray and to approach God's presence.
And it set detailed laws, practices and traditions for us forever.

Answer 2

God revealed his presence to the Israelites on Mount Sinai (Exodus 19-20), to give them the Ten Commandments (ibid).

These Ten Commandments are a pillar of Western civilization. They have improved the conduct of billions of people; but because of His covenant with them (Exodus ch.24), God specifically honored the Israelites with being the nation which would be the ones to receive and treasure the Ten Commandments until they had been absorbed by humanity in general. These Commandments are so important that God spoke them out loud to the whole assembled nation; and He inscribed them in stone (Deuteronomy ch.9); unlike the rest of the Torah, which He had Moses write (Deuteronomy 31:24).

What would Western society look like without these Commandments?

1) "I am the Lord your God..." has shaped the Western beliefs about God. Pantheism and polytheism, which were excuses for immorality, are out.
2) The 7-day week, including a day of rest for everyone, is thanks to the Fourth Commandment.
3) Without the Fifth Commandment, society might still permit abandoning our aged parents to die.

4) Without the Sixth Commandment, we might still be killing our own children, as was done in Classical European nations until Judaism and its daughter-religions put a stop to it. The above are just a few examples.

See also:

How has the Hebrew Bible influenced Western society?

What is the history of the Hebrew Bible?