Or HaGanuz
The Gemara (Chagigah 12.) says, "With the light that Hakadosh Baruch Hu created on the first day of creation, a person could see from one side of the world to the other." This light wasn't the light of the sun because the sun was created on the fourth day of creation, and this was still the first day of creation. It was a unique light, about which it states (Bereishis 1:4), ויבדל טוב כי האור את אלקים וירא אלקים, "Hashem saw the light that it was good, and Hashem separated it..."
The Gemara says, "When Hakadosh Baruch Hu thought about the generation of the flood and the generation of dispersion (הפלגה דור), and He saw their corrupt ways, Hakadosh Baruch Hu immediately concealed the light from them. This is as it states (Iyov 38:15) אורם מרשעים וימנע, 'Their light shall be withheld from the wicked.' For whom did Hashem store the light? For the tzaddikim of the future... When the light saw that it was being reserved for tzaddikim, it was happy, as it states (Mishlei 13:9) ישמח צדיקים אור, 'The light of the tzaddik will rejoice.'"
Where was this light concealed? The Baal Shem Tov zt'l says that this holy, concealed light is concealed in the Torah. One can tap into this sacred, concealed light when studying Torah. Another time to connect with this holy light is when we light Chanukah lecht. The Bnei Yissaschar (Kislev 2:21) writes, "I have brought you the testimonies of three trustworthy witnesses that the light of Chanukah is the Or HaGanuz (concealed light of creation). They are (1) the holy tzaddik, the Rokeach, who received his lessons from Eliyahu HaNavi z'l. (2) The Maharal of Prague. It is known that his teachings were said with ruach hakodesh, and he would use Sefer Yetzirah. (3) And the holy Rav, who lived close to our times and was renowned for his ruach hakodesh, Rebbe Pinchas of Koritz zt'l."
Chazal hardly mention Chanukah. The Zohar mentions Chanukah once (vol.1 238:); the same is true with Tikunei Zohar (29.). Even when they mention Chanukah, it is a side topic, not the primary issue being discussed. This is because Chanukah is the concealed light, the Or HaGanuz, so it was also concealed in the Oral Torah. But as we approach the geulah [when the Or HaGanuz will shine], tzaddikim began to speak about the mitzvah of Chanukah lecht, ideas that gedolim of previous generations didn't imagine.... They began to reveal that the light of Chanukah is the concealed holy light, the Or HaGanuz.
The Gates of Salvation
The Bnei Yissaschar (Kislev-Teves 4:65) writes that the gates of Gan Eden are closed at night, but it seems from the teachings of Reb Pinchas Koritzer that when Yidden light Chanukah lecht, the gates of Gan Eden open.
The number and the name of the simanim in Shulchan Aruch are associated with the mitzvah that siman discusses (as is brought down in Agra d'Pikrka, Naso, regarding the mitzvah of Viduy, and several other sources teach this idea). The Beis Yisrael zt'l said that Hilchos Chanukah begins with siman תרע, which is similar to א"תרע, which means "gate" in Aramaic. This hints that the gates of salvation open when we light the Chanukah lecht. The Gemara (Bava Kama 80:) states, "When a door is locked, it won't open so quickly" We understand that the opposite is undoubtedly true; when the gates of heaven and salvation open, they won't close so quickly, and we will merit all kinds of salvations, beyond the rules of nature. The Beis Yisrael zy'a adds that the gates of heaven are opened on Chanukah, and everyone can enter.
