In Lithuania before the second world war, the mussar movement was very widespread. There was a popular expression that a Jew has to be "ehrlich" and only a galach has to be "frum". “Frum” was, in a certain sense, a dirty word; the connotation of the word was outward demonstration of one’s religiosity. There is a well-known Gemara at the end of Makkos which says that six hundred and thirteen mitzvos were given to Moshe Rabbeinu at Har Sinai, and eventually the prophet Michah singled out three specific issues that one should be careful about which would lead one to observance of all six hundred and thirteen mitzvos. The passuk quoted in that Gemara is the concluding line in the haftorah of Parshas Balak, “ki im asos mishpat v’ahavas chessed v’hatzne’ah leches - doing justice, loving chesed and leading one’s life in the fashion of tziniyus” (Micha 6:8). The Gemara did not mean to say that the only mitzvos one must observe are these three matters. The simple meaning is that observance of these three will lead one to observing all the six hundred and thirteen mitzvos. The Gemara in Sukkah points out that it is usually expected at a funeral or wedding that there will be a public demonstration of emotion. However, because the aforementioned passuk in Michah uses the term "leches" (“v’hatzne’ah leches”) and the passuk in Koheles (7:2) refers to weddings and funerals by using that same verb (leches - “tov la’leches el beis ovel mi’leches el beis mishteh”), even at weddings or when one is delivering a eulogy at a funeral, one should not overdo in public expressions or demonstrations of one's emotions.
The concept of tznius is often misunderstood. Many people think that it only applies to women in the way that they dress. This is clearly incorrect. The mitzvah applied equally to men and to women. Yeshaya haNavi (45:15) describes Hashem as being a Keil mistater. Hashem does such a good job at hiding that many think that he does not even exist. The Torah tells us that man was created b'tzelem Elokim, possessing all the middos of elokus. The Jewish people were instructed, “vehalchta bidrachav” (Devarim 28:9), i.e. that we must imitate the ways of Hashem in order to preserve that tzelem Elokim which is already in our personalities from birth. We cannot be invisible like Hashem, but we should try as much as possible to lead our lives b'tzinah as opposed to b'farhesya.
The Mesilas Yesharim describes two different people who want the public to know that they are here: one gets an aliyah and screams out the berachos louder than anyone else, and one who gets and aliyah and whispers the berachos and no one can hear him. Both are doing something irregular in order to draw attention to themselves. Some students come into a beis medrash every day with a loud colored sweater. The sweater is screaming out loud: take notice of me, I am here!! The whole idea of tznius is to dress, speak, and act in an inconspicuous fashion, to lead one’s life b'tzinah as opposed to b'farhesya. This concept is one of the three singled out by the navi Michah which will help us observe all of the other six hundred and thirteen mitzvos.