Shortly before sundown on the 29th of Adar, G-d commanded Moses regarding the mitzvah of sanctifying the crescent new moon and establishing a lunar calendar. This is the first mitzvah the Jews were given as a nation.
Moses had difficulty envisaging the moon's appearance at the exact moment of its monthly rebirth. After the sun set, G-d showed Moses the crescent new moon of the new month of Nissan, showing him the precise dimensions of the moon at the moment the new month is to be consecrated.
For the generations that followed, each new month was ushered in when two witnesses testified before the Sanhedrin (rabbinic supreme court) that they had seen the molad, the new moon. In the 4th century CE, Hillel II foresaw that the Jews would no longer be able to follow a Sanhedrin-based calendar. So Hillel and his rabbinical court established the perpetual calendar which is followed today -- until Moshiach will come and reestablish the Sanhedrin.
Links::
Lunar Time
Rosh Chodesh
The Molad
A few months after its creation, Napoleon's "Sanhedrin" (rabbinical supreme court) was dissolved. The Sanhedrin was created to approve certain religious regulations requested by the French "Assembly of Notables." The regulations were designed to blur the distinction between Jews and non-Jews.
The rulings of this pseudo-Sanhedrin were never adopted by Jewish communities.
Link:: Napoleon Bonoparte
We are one because we share a single soul, like a single, brilliant sun shining into many bodies. Since the soul is what counts, that makes us essentially one.
That is the meaning of the mitzvah of the Sukkah—a place that encompasses us all equally, rendering us a single whole.
We are also one because none of us are alike. Each of us reflects a different facet of that same soul, each of us with our strengths and our weaknesses, so that we all need one another to be whole and complete.
That is the meaning of the mitzvah of the Lulav, the Etrog, the Hadassim and the Aravot—four very diverse species, each containing that which the others lack.
And that is why this mitzvah is best done inside the Sukkah: To draw the oneness of our shared soul into the harmony of our diverse bodies.