The verse immediately following the account of the giving of the Ten Commandments to Israel by G-d at Mt. Sinai, which summarizes the experience of that greatest of all days, reads: "And the whole people saw the voices and the torches and the shofar blast and the smoking mountain…" (Exodus 20:15).
In Kabbalah, we are taught that the four levels of the peoples experience–
seeing the voices
the shofar blast
the smoking mountain
–correspond to the consummate experience of the four components/letters of G-d's Name:
The opening verb of the verse, "and the whole people saw" (literally, "seeing," in the present tense), refers in general to all the four levels of the verse, but in particular refers to the first of the four: "seeing the voices" (and refers to the words spoken by G-d, as noted by Rashi). Our Sages take this to mean that when the Torah was given to Israel, the experience of Divinity of G-d's absolute Oneness was so intense that it unified and synthesized the human senses of seeing and hearing: "seeing the heard and hearing the seen." This reflects the level of Divine wisdom in the soul–chochmah, the yud of G-d's Name–which is the only power of the soul which perceives directly Divine unity.
"The torches" represent the inner flame of the soul, its desire to return and become consumed in G-d's Infinite Light. This is the experience of the depth of understanding and meditation, binah, the higher hei of G-d's Name.
In Chassidut we are taught that "the shofar blast" represents the Divine power to "bring down" and impress the words of G-d on the heart of man. The shofar blast causes the heart to first tremble in awe of G-d, and thereafter to desire with all the strength of one's emotions to live by G-d's word and walk in His path. The root of the word shofar means "to improve"–the source of motivation in the heart to ever improve and progress in one's fulfillment of Torah. This level of Divine experience corresponds to the midot, the emotions of the heart, the vav of G-d's Name.
The first three levels of Divine experience at Sinai are all revelations from above. The final, consummating level of the experience is "arousal from below"–the "smoking mountain." The word "smoking" (ashein) is explained in the Kabbalah to be an acronym for the three all-inclusive dimensions of (physical) reality: "world" ("olam" = space), "year" ("shanah" = time) and "soul" ("nefesh" = living human body). The mountain itself symbolizes the lowest of the physical elements of creation, earth, uplifting itself towards heaven.
To see the mountain "smoking" is to experience the Divine spark innate in all dimensions of physical reality, arousing itself in desire to return to G-d, the Creator. This corresponds to malchut, the final hei of G-d's Name (referred to in Kabbalah and Chassidut as "the lower teshuvah" in contrast to the "higher teshuvah" of the first hei of G-d's Name, described above).
When we stay up on Shavuot night, we are all able, each and every one of us on his or her own level, to re-experience the giving of the Torah at Sinai. The mystery of G-d's Ineffable Name becomes engraved on the essence of our souls. In all facets of our lives, we become able to experience His Absolute Unity, the "return" of our finite consciousness to His Infinite Light, the walking in (i.e., emulating) His ways, and the elevation of all creation to recognize its Creator.
With this rectified consciousness we proceed to become true vessels, with open eyes, to behold the revelation of Moshiach and the true and complete redemption of all reality. May we merit this–this year, Amen!