A righteous Yid once stopped by the roadside to daven. A powerful minister came riding by and greeted him, but he did not reply. The minister waited for him to finish and then screamed: "Good-for-nothing that you are! Doesn't it say in your Torah that you should guard your life? So why didn't you return my greeting? I could have chopped off your head with my sword!"
The Yid replied with a question, "If you were standing in front of a king, and your friend passed by and greeted you, would you return the greeting?"
"Of course not!" said the minister.
The Yid continued, "And if you did return the greeting to your friend, what would the king have done to you?"
"He would have chopped off my head!" said the minister.
The Yid concluded, "How much more so does this apply to the King of Kings, Who is eternal!" The minister was appeased and the Yid continued his journey in peace. (ברכות לב ע"ב)
In a letter to his chassidim, the Alter Rebbe explains why davening is likened to standing before a king. If a person standing before a mortal king busies himself with his own matters, he is publicly displaying his foolishness. Moreover, by publicly insulting the king he is forfeiting his life. But what if a person lacks the sensitivity to appreciate the awesome privilege of beholding the king in all his glory? He, too, should at least conduct himself with respect when in the royal presence. How much more so does this apply to the eternal King. (אגה"ק סי' כד)
One must give close attention to the responses to Kaddish, for its holiness is even greater than that of Kedusha. Even during Shemoneh Esreh one should pause and listen to Kaddish [until the end of the sentence, "Yehei shmei rabba..."]. Those who speak during Kaddish should be admonished, even if there is a minyan present without them.
During chazoras hashatz one should concentrate and listen to the brachos of the chazzan. It is forbidden to talk, recite Tehillim or learn, even if one answers Amen. Those who do otherwise should be admonished.
If someone engages in mundane conversation during chazoras hashatz, his transgression is too great to bear, for by speaking while the congregation is involved in praising HaShem, he is showing that he has no connection to Him. (שו"ע אדה"ז סי' נו ס"א וס"ד, סי' קד ס"ה, סי קכד ס"ו וס"י)
In order to ensure silence during davening, the Alter Rebbe enacted a decree that no idle talk should be spoken from the moment the sheliach tzibbur begins until the end of the last Kaddish. This applies during Shacharis, Mincha and Maariv. (אגה"ק סי' כד)
Showing Reverence
The Zohar writes that by speaking during davening one implies that he does not believe HaShem is in shul, for if he did, he surely would not talk.
The Smak says that we ought to deduce a kal vachomer from the way idolaters conduct themselves in their places of worship: throughout their prayers, they stand in silence. How much more so does this apply to us, who stand in the presence of HaShem. (זהר תרומה קלא ע"ב, סמ"ק מצוה יא, ועד"ז בס' חסידים אות יח)
When Satan complains that Yidden commit aveiros, HaShem rejoins that if the goyim had accepted the Torah, they would have been far worse. However, when Satan argues that Yidden converse during davening, this response does not apply.
A hint for this can be found in the possuk, "HaShem yilacheim lachem v'atem tacharishun." The pshat, of course, is that "HaShem will fight your battle, and you shall remain silent." In addition, on the level of derush, that possuk is hinting that HaShem will protect us – on condition that we remain silent and refrain from idle talk during davening... (דרך משה, רב ייבי בקונ' מורא מקדש)
The two great students of the Baal Shem Tov – Reb Yaakov Yosef ("Reb Yeivi") of Ostroho and Reb Pinchas of Koretz – couldn't agree: What was the issue that needed the most urgent attention? Reb Yaakov Yosef held that it was the habit of idle conversation during davening, so he would go around and constantly arouse people to refrain from talking in shul. Reb Pinchas held that the most widespread problem was the lack of tznius, and he focused his efforts on correcting that.
One day, while they were debating this question, each trying to convince the other that he was right, they finally agreed that they would open a Chumash at random, and the first possuk to catch their eye would indicate who was right.
They opened a Chumash Bereishis, and immediately saw the words of Shimon and Levi concerning Dina: "Should he deal with our sister so grossly?!" A victory for Reb Pinchas!
"Wait," said Reb Yaakov Yosef. "Let us look at the explanation written in Targum Yonasan." Sure enough, there it is written: "It is not proper that it be talked about in the shuls that... idolaters defiled the daughter of Yaakov Avinu..." (סיפורי חסידים זוין תורה ע' 125)
Sometime around the year 5705 (1945), the Rebbe entered the shul at 770, stood at the bima, and announced that he had just come from speaking with his father-in-law, the Frierdiker Rebbe, who had asked him to convey the following message: "My father (the Rebbe Rashab) was with me and asked, 'How does it come to pass that in your beis midrash people talk during kerias haTorah?' " (קדושת הדיבור ח"ג ע' 129)
Consider
Why shouldn’t one talk during davening: for the sake of others, for himself or for HaShem?
