Rabbi Herschel Schachter
The Breaking of the Glass
In expressing His affection for the Jewish people, G-d refers to them with all loving terms of familial relationships. He calls them His daughter, His sister, and His mother (Shemos Rabba 52:5). But above all, He refers to the Jewish people as his darling bride. The entire book of Shir Hashirim depicts the special relationship between Hakadosh Baruch Hu and His people as one of a marriage. Regarding all other relatives the halacha distinguishes between various degrees of closeness: rishon b'rishon; rishon b'sheni; shei b'sheni; etc. (see Shulchan Aruch, Choshen Mishpat 33:2). Regarding a husband and wife, the closeness of the relationship is considered as one of "ba'al dovor". Ba'al ke'ishto implies that the two are considered one entity; as the possuk in parshas B'reishis (2:24) states, "Ve'hayu le'bosor echod." The Zohar  uses such an expression to describe the relationship between G-d and His Jewish people: Kudsha Brich Hu ve'Yisroel chad hu - they are one! The expression used in Parshas Bereishis to describe the closeness of a married couple, "ve'davak beishto" (2:24), appears again in the Torah describing the relationship expected of each Jew towards G-d, "u'vo sidbak" (Devorim 10:20). This very special level of relationship was established through the giving of the Torah at Har Sinai.
The very first possuk that we teach every Jewish child when he is able to speak is, "Torah tzivah lano Moshe, morasha Kehillas Yaakov"(Devorim 33:4, Sukkah 42a), and the rabbis (Sanhedrin 59a) recorded the tradition that the word "morasha" has a double meaning: the simple meaning of the phrase is that the Torah is the national heritage of all the Jewish people . According to the additional meaning, the word "morasha" implies also "me'urasah", meaning a marriage. All of the Jewish people are married to the Torah, and through mattan Torah the marriage between G-d and the Jewish people was accomplished.
The Tashbetz (#465), who records the minhagei Ashkenaz, writes, "hold on to this rule, all of the customs of the Jewish marriage ceremony have their sources in mattan Torah." The Maharam of Rothenberg is quoted (#464) as having translated the expression "Harei at mekudeshes li kedas Moshe veYisroel", as, "I hereby marry you, just as the Jewish people are married to the Torah." We are married to the Torah, and thereby married to G-d! 
The Torah is a representation of G-d's essence,  and therefore the full quote of the Zohar really reads that "G-d, the Torah, and the Jewish people" are one. What it means is that through our receiving the Torah, we became united "in marriage" with G-d, to become one entity.
In addition to all the many customs practiced at a Jewish wedding which are known to be patterned after ma'amad Har Sinai , Rav Soloveitchik added the following: the common practice is that the groom (or someone else in attendance) breaks a glass. Many assume that this is to remind all those in attendance of the destruction of the Beis Hamikdash , and is based on the possuk in Tehillim (137:6) which encourages all to always make mention of Jerusalem at all times, even on the joyous occasion of a wedding. In the Talmud (Brachos 30b, 31a), the source of the custom, this practice is really recorded in a different context: even when one rejoices, the cheerfulness should always be toned down a bit (vegilu bireadah) lest it lead to levity.
Rav Soloveitchik said in the name of one of the Geonim  that the breaking of the glass is also reminiscent of ma'amad Har Sinai. The medrash  points out that because the first luchos were given with great publicity and fanfare, this had a negative effect, and caused them to be broken. The second set of luchos was given privately (betzinah) and therefore it lasted. Through this contrast, the Torah teaches us the lesson of tznius, of always leading a private life. G-d is described by the prophet Yeshaya (45:15) as a Kel Mistater, as one who is in hiding. We were all created "in his image" and commanded to preserve that "tzelem Elokim" by leading our lives in the "ways of G-d" . We break the glass at the wedding to impart to the young couple that they must lead a life of tznius, otherwise their marriage may suffer, just as the first set of luchos was smashed!
The Rema writes (Shulchan Aruch, Even Hoezer 21:5), based on the story related in the Talmud (Bava Basra 58a), that it is not appropriate for a married couple to hug or kiss or otherwise demonstrate spousal affection in public. Similarly it is highly improper for a mother to nurse her baby in public, even without exposing her body .
The midda of tznius, however, includes much more than that: one should not wear loud-color clothing to draw attention to oneself, nor speak in a very loud tone of voice, or in an exaggerated soft tone, either of which would accomplish the same result. One should not walk in public in a fashion that will draw attention, either very slowly or very quickly; in a very erect posture, or with a stooped over posture. One should not furnish his home or act in public in an ostentatious fashion . One should always lead a private, hidden life. The word tznius has the same meaning of betzin'ah - in hiding.
On Yom Ha'atzmaut of 1958, Rav Soloveitchik delivered a talk  where he quoted in the name of Rav Meir Shapiro (the rabbi of Lublin, and the founder of the famous Yeshiva there) that G-d knew in advance that His spectacular public appearance at the occasion of ma'amad Har Sinai would certainly carry with it negative effects (i.e., the smashing of the luchos). Nonetheless He felt that under the circumstances it had to be done in that fashion , in order to make the havdalah (distinctiveness) of the Jewish people very noticeable. Unlike the general distinction between kodesh and chol (as between Shabbos and the weekdays), which is usually not discernable to the average eye, G-d wanted the havdalah of the Jew to be obvious and apparent.
Veholachta bedrachav dictates that just as G-d on occasion, so to speak "beshaas hadechak", feels compelled to come out of His hiding and anonymity, so too, on occasion we are also called upon, as an exception to the rule, to do certain mitzvos in a public demonstrative fashion. But this exception to the rule should not detract from our proper understanding of the rule, namely, that in principle, each Jew should attempt, to as great an extent as possible, to lead a hidden and a private life.
 This is the famous interpretation of the Ravad to the passage in Sanhedrin (9b, 10a)
 Often quoted in Nefesh Hachaim by Rav Chaim of Volozhin.
 See Nefesh Harav, pg.7
 The Talmud (Shabbos 86b) records a tradition that was shared by all the tanaim, that ma'amad Har Sinai occurred on Shabbos. Some rishonim understand that due to this, every Shabbos we (the Jewish people and Hakadosh Baruch Hu) celebrate our wedding anniversary! This is how they understand why in the shacharis shmoneh esrei of Shabbos we speak of ma'amad Har Sinai. The couple celebrates "their anniversary" by retelling the story of their marriage.
The Talmud (Sanhedrin 58b) points out that it is not permissible for a non-Jew to observe Shabbos. The Zohar explains this law by way of a parable: the maid in a royal palace has the keys to all of the rooms, and is expected to keep everything in good shape. However, when the king is having an intimate encounter in the bedroom with the queen, if the maid will barge in at that time, she will have her head handed to her. Shabbos is the day on which we (the Jewish people and Hakadosh Baruch Hu) celebrate our wedding anniversary, and there is much more intimacy than all week long, and non-Jews intruding on that privacy are likened to the maid in the parable.
All year long the text of the Shmone Esrei for Shacharis, Mincha, and Maariv is the same. The same is true on yom tov as well. On Shabbos, however, each of the three tefilos has a different text. The Avudraham explains this by pointing out that the marriage ceremony consists of three parts: the kiddushin, the chuppah, and the yichud. On Friday evening in Maariv we recite Atta kidashta, to reminisce about our kiddushin with Hashem. On Shabbos morning in Shacharis we speak of ma'amad Har Sinai, at which time Hashem was kafah aleihem har kegigis, which served as our chuppah. And finally, at Mincha, towards the end of Shabbos, we reminisce about Atta echod, about our yichud (with Hakadosh Baruch Hu), which always follows the chuppah.
 The candles and the music are reminiscent of the "kolos" and the "brokkim"; the seven brochos correspond to the seven "kolos" of Har Sinai; and many more. See Tashbatz #464
 See Rema to Orach Chaim (siman 560)
 I was not able to locate any written source for this quote. However, a similar idea is quoted in seforim in the name of Rav Nachman of Breslav, that the custom to interrupt the chosson in the middle of his dvar Torah is to remind us of the smashing of the luchos, and I once heard from Rav Gifter that perhaps this is the idea he was trying to bring out.
 Tanchuma to Parshas Kisisa, end of #31
 This was a recurrent theme in the public lectures of Rav Soloveitchik. See the volumes Yemei Zikaron (1986), pgs. 50-52; Divrei Hagos V'ha'aracha (1982), pg. 174-175. See also Nefesh Horav pgs. 1 and 281, and my two previously published essays on TorahWeb.org - "On the Matter of Masorah" and "Can Women be Rabbis?"
 For a discussion of the ramifications of a woman violating the principles of tznius, see Talmud Ksubos 72a and 72b, and Tshuvos Lev Aryeh (Grossnass), vol. 1 #30, quoting Rav Boruch Ber.
 See Rambam, Hilchos Deos (5:6-8).
 See Mipninei Horav, pg. 301-302
 Halacha has a principle that shaas hadchak k'dieved dami; that beshaas hadchak we allow lechatchila that which normally is only acceptable bideved.