There was the world before Mattan Torah, and the world after Mattan Torah.
The world before Mattan Torah was one in which people believed in a multitude of false gods; the heavens were crowded with them and idols stood on every mountain and hilltop.
The world after Mattan Torah was one in which an entire people attested to the existence of only one G-d, Who created the sun, the moon and the stars, and fashioned every high place in accordance with His Will.
In the world before Mattan Torah, power ruled and cruelty prevailed; after Mattan Torah, Hashem made known that the world is built on love and kindness. That is why in the blessing Sim Shalom we speak of Toras chaim v’ahavas chessed, because the living Torah revealed at Sinai came with the revelation that Hashem created the world in order to perform kindness, to give to others (Chofetz Chaim). That, too, is one of the reasons for reading Megillas Rus on Shavuos, to remind ourselves that Torah and chessed are inseparable.
Before Mattan Torah, the concept of the duality of the physical and the spiritual prevailed; sacrifice and prayer belonged to the upper worlds; eating and drinking belonged to this lower world.
Then Hashem descended upon Mount Sinai (Shemos 19:20); He lowered the Heavens to the Earth and spoke with us from the mountain. We were given to understand that holiness can be attained in this world, in this life of eating and drinking.
That is why, explains the Vilna Gaon, the mouth, the organ of speech, which distinguishes man from the animal, is also the orifice of ingestion. The mouth, like the mind, is a vessel for holiness. That is why it is situated in the upper part of the human body, even though digestion takes place in the lower part. Because eating and drinking sustains the body in order to serve Hashem (Gra, Biurei Aggados, Sanhedrin 39a).
Before Mattan Torah, the ancients believed that after death the individual becomes part of the cosmos; personal identity and self-awareness are obliterated forever.
After Mattan Torah, we understood that the neshamah itself derives from eternity and lives on, eventually to be reunited with the guf. Our inheritance is not oblivion, but a more exalted perception of the Source of life than anything we can imagine here on Earth.
Before the Torah was given, the Jewish people were already more than a mass of humanity or an aggregation of families; they were a nation, welded together by the shared experience of slavery in Egypt.
But at Sinai — the culmination of a journey in teshuvah that began at Rephidim — they became as one person with a single heart (Rashi, Shemos 19:2). A nation united not by territorial borders and legal constructs, and by more than language and history.
Klal Yisrael became of one heart — such that words that issue from the heart enter the heart. A Jew who speaks from the heart connects with that great organ of being shared with every other Jew (Rav Eliezer Kaplan, Mashgiach, Yeshivas Radin).
But perhaps the greatest marvel of Sinaitic unity was that even though all heard as one the same voice of Hashem uttering the Aseres Hadibros, the individual did not dissolve into the mass.
“If it had been written kol Hashem b’kocho, the world could not have withstood it. Rather, it says, kol Hashem b’koach — according to the capacity of each individual (Shemos Rabbah 29:1).
They all heard exactly the same words. But when they did chazarah, reviewed together the immortal precepts still echoing in their ears, they discovered that each person had a different understanding of them.
In Derech Etz Chaim, Harav Moshe Chaim Luzatto says that there were 600,000 peirushim on the Torah, each peirush reflecting the root of the person’s neshamah. And yet, Anochi Hashem Elokecha seals the Aseres Hadibros, to make known that, despite the differing interpretations, all are based on the same Source. That was the great marvel: A perfect national unity, yet without sacrificing the individual (Rav Shlomo Wolbe, Alei Shor, Vol. 2, pp. 399–400).
However, the perfect unity the Jewish people had achieved held only for that moment in history. The world after Mattan Torah did not remain at that spiritual height; controversy and rebellion soon made their reappearance with the Meraglim, Zimri and Korach. The difference between the world before and after Mattan Torah was obscured as well. Most of humankind continued to live as before.
May the experience of Shavuos inspire us to live more in the world that Hashem revealed to us — the world after Mattan Torah.