ויקרא פרק ט, כב וַיִּשָּׂא אַהֲרֹן אֶת-(יָדָו) [יָדָיו] אֶל-הָעָם וַיְבָרֲכֵם
The verse about Aharon blessing the people is written ידו (singular-hand), but is read ידיו (plural-hands). This could be the source for the custom of the Cohanim to join their two hands together to appear as if they are one hand.
ויקרא פרק י, א וַיִּקְחוּ בְנֵי-אַהֲרֹן נָדָב וַאֲבִיהוּא אִישׁ מַחְתָּתוֹ וַיִּתְּנוּ בָהֵן אֵשׁ וַיָּשִׂימוּ עָלֶיהָ קְטֹרֶת וַיַּקְרִיבוּ לִפְנֵי ה' אֵשׁ זָרָה אֲשֶׁר לֹא צִוָּה אֹתָם:
The Gemara (Eiruvin 63a) states that the sons of Aharon only died because they taught a law in front of their teacher (Moshe). At first glance this appears to be a punishment since they slighted the honor of Moshe.
This is difficult since we see in the case of Chuldah that she prophesized about the future. And the Gemara (Megillah 14b) asked how did she do this in the area of the established prophet Yirmiyahu and was not punished? The Gemara answered that Chuldah was a relative of Yirmiyahu and thus, he was not bothered and, thus Chuldah was not punished.
Therefore, in our case Moshe also should not be bothered since the two sons of Aharon were also his nephews, and Moshe would have surely pardoned his honor. So why were they punished?
We must say, however, teaching a law in front of one’s Rebbe has the additional problem of appearing like a denier of the transmission of the faith, which is not subject to m’chilah.
ויקרא פרק י, ג וַיֹּאמֶר מֹשֶׁה אֶל-אַהֲרֹן הוּא אֲשֶׁר-דִּבֶּר ה' לֵאמֹר בִּקְרֹבַי אֶקָּדֵשׁ וְעַל-פְּנֵי כָל-הָעָם אֶכָּבֵד וַיִּדֹם אַהֲרֹן:
The Gemara (Z’vachim 115b) states about the silence of Aharon, that he received reward. The Gemara brings a proof from Koheles (3:7) “a time to be quiet and a time to speak”. This verse implies that at times one is quiet and is rewarded, and at other times one speaks and is rewarded. The Gemara does not explain what these times are and says פעמים, which indicates multiple times or a frequent set of circumstances (and not just the one time that Aharon was silent).
Perhaps, the “reward for silence” could be applied to the times when one visits with a mourner, and nothing needs to be said, that the comfort derives from the shared silence. Thus, in the first three days of mourning when visiting, the visitor should be silent until the mourner speaks.
Whereas, the time of “reward for speaking” involves the time at a wedding simchah. At a wedding, one should speak words of praise regarding the couple in order to endear them to each other and those surrounding them. And regarding these words, one receives reward (one that makes happy newlyweds receives the reward of meriting Torah).