The Gemara in Masechet Shabbat 88b, tells the story of how Moshe Rabbeinu ascended to the Heavenly heights. The ministering angels were at first annoyed to see a man of flesh and blood in their domain. They asked Hashem what he was doing there.
He explained that Moshe had been summoned to receive the Torah. This made the angels even more upset, as they felt that the Torah had such a high level of holiness that it belonged in the Heavens.
Hashem then told Moshe to respond to the angels justifying that the Jewish people were worthy to receive this sacred gift. After being told to hold on to the כסא הכבוד, throne of glory, Moshe responded.
He said that G-d’s existence was learned from the words, “I am the L-rd that took you out of Egypt.” Were the angels taken out of Egypt.
He continued by asking if the angels were ever tempted with idol worship. Did the angels work so hard that they needed a day of rest. Were they involved in business transactions where they might take Hashem’s name in vain.
Did they have the same temptations of man that needed to be overcome? Did they have jealousy or a יצר הרע, evil inclination, that needed to be overcome?
The angels were impressed and greatly respected Moshe from that day forward.
This little story makes it abundantly clear, how badly the Jewish people and the whole world, desperately need the teachings of the Torah. If man is left to decide right and wrong on his own, he will self destruct.
This is the main reason for the celebration of Shavuot. We acknowledge and show our appreciation, for being given this precious gift of the Torah.