Every month in the Jewish calendar represents a unique way to serve Hashem. This is exemplified in its central theme and its numerical place in the order of the year.
The central theme of the “third month” is Matan Torah, the giving of the Torah to the Jewish people. There are two ways to count the months of the Jewish year – beginning with Nissan or beginning with Tishrei. Biblically the first month is Nissan, and Sivan is the third month. When counting from Tishrei, Kislev is the third month of the year.
In Sivan, on Shavuos, we received the Written and Oral Torah through Moshe Rabbeinu on Har Sinai. According to the Talmud, the three parts of Tanach (Torah, Nevi’im and Kesuvim) were given to the nation of three people (Kohanim, Levi’im and Yisroel), through the third person (Moshe Rabbeinu was the third child in his family), on the third day of preparation for receiving the Torah.
In the month of Kislev, the other “third month,” the Jewish people received the hidden Torah, the wellsprings of Chassidus. Although Chassidus, the secrets of Torah, were included in Matan Torah, they were not revealed to the people at large. On the 19th of Kislev, with the liberation of the Baal HaTanya, Rabbi Schneur Zalman of Liadi, the light of Chassidus won out over the darkness of the Soviet empire and was allowed to be freely spread across the world. Thus, the 19th of Kislev was the Matan Torah of Chassidus.
The festival of Chanukah occurs in the third month for a reason. It is written in the Midrash that the Mishkan was finished in the month of Kislev, but it was not erected until Nissan. Since Kislev did not get the recognition for the completion of the Mishkan, G-d promised to give Kislev a dedication of its own, and He made the Chanukah (dedication) of the Beis HaMikdash by the Maccabees occur in Kislev. This dedication was the rededication of the Second Beis HaMikdash, which is actually the third Sanctuary if you count the Mishkan built by Moshe Rabbeinu, connecting it to the number three.
The rededication of Chanukah was necessary, because the Greeks defiled the Beis HaMikdash. When the Maccabees restored the Beis HaMikdash to its glory, they enabled the revelation of G-dliness, the eternal illumination of the darkness through the Chanukah lights. This is the central theme of Kislev. This illumination is also linked to the revelation of Chassidus in the month of Kislev, because the light of Chassidus came out of the darkness of exile in Russia.
Just as we light the Chanukah menorah at the entrance to our homes to light up the darkness outside, Chassidus illuminates the darkness of our world through the Baal Shem Tov’s promise: “Your wellsprings will spread forth to the outside.” When all of the darkness has been converted into light, the illumination will be so great that the world will shine with G-dliness and Moshiach will bring us into Geulah.