"And Elokim said, 'Let there be Light'..."
On this pasuk, the midrash in Bereishit Rabba says this: R' Shimon said to R' Shmuel that he had heard that R' Shmuel was a master of Aggada and asked him where this light was made? R' Shmuel answered that Hashem was dressed in the light like clothing (as the pasuk in Tehillim says, "…wrapped in Light as in a garment..."), and that His glorious light illuminated from one end of the world to the other, and that he was taught this through whisper. R' Shimon asked him why he needed to hear this through a whisper when it's an explicit pasuk! R' Shmuel said that just as he heard it through whisper, so too he had to say it in a whisper.
The Torah is given in three ways: through loud thunder, regular speech, and whispering. The modes of transmission corresponds with different sets of needs in the receiver. One who is hard of hearing requires loud, thunderous words. One who has a very sensitive ear needs a whisper. One with regular hearing receives regular speech. The form of the transmission is guf (body), and the content of the transmission is neshama (soul, specifically rational-linguistic soul). The thunder has a powerful guf. The whisper has very little guf, its substance is almost entirely neshama. When one who is hard of hearing is given a whisper, or one who is very sensitive is given a thunder clap, there may be destruction.
In Egypt, Bnei Yisrael (The Children of Israel) built up resistance to the spiritually assaulting environment. So, when we arrived at Mount Sinai, we were hard of hearing and numb to Hashem's Torah. In order to receive the Torah, Hashem communicated in a loud and thunderous way, waking us up and shaking us from our spiritual slumber. After that initial awakening, the booming became unnecessary. In the thunder, not only was content transmitted, the bodies of the receivers were transformed by the body of the transmission.
The Torah prohibits Kohanim (high priests) from drinking wine while working in the Beis Ha-Mikdash (Temple). This may be counter-intuitive at first. After all, didn't King David write, "Yayin y'samach l'vav enosh," wine makes the heart of man happy, and isn't the Temple a place of great happiness? The Zohar explains why wine is forbidden to the Kohanim: there are two types of drink, Wine and Oil; Wine brings out the voice of man, and oil softens it. Kohanim cannot drink wine in the Beis Ha-Mikdash because the loud voice which it brings out is painful against the sublime sensitivity within the Beis Ha-Mikdash. Furthermore, when the Kohen Gadol goes into the Holy of Holies, the most sensitive place in the whole Beis Ha-Mikdash, he uses oil to light the Menorah. This shows the mode of transmission in the Holy of Holies-whispering. Also note, the originator of the Zohar, the great, fantastically sensitive mekubal (receiver) of Torah, R' Shimon (from the midrash above), is compared to oil in a liturgical poem.
A person, who strives and yearning for the deeper facets of Torah, must enter that place where the thunderous voice is not allowed and the quiet whisper of Hashem is found. This one enters the Holy of Holies and finds the light from the Menorah filled with oil. This depth is not given in a voice-the more neshama, the less guf. These depths are accessed in whisper. On Chanuka when we light with oil, we are contacting the neshama, the deep inner point, of what Hashem is whispering to us. The 25th word of the Torah is "light" (in "And Elokim said, 'Let there be Light'..."). This correlates with the starting date of Chanukah, the 25th of Kislev. The light of Chanukah shines forth from the quiet whispers of Hashem for those who long to hear. Amidst the darkness of the exile and its winter, arises a deep cry to all of us to meet this light and to hear His whisper. May we all merit this awesome light in these quiet nights.
(Based on shiurim by R' Lopiansky)