(א) וַיִּקְח֣וּ בְנֵֽי־אַ֠הֲרֹן נָדָ֨ב וַאֲבִיה֜וּא אִ֣ישׁ מַחְתָּת֗וֹ וַיִּתְּנ֤וּ בָהֵן֙ אֵ֔שׁ וַיָּשִׂ֥ימוּ עָלֶ֖יהָ קְטֹ֑רֶת וַיַּקְרִ֜בוּ לִפְנֵ֤י יְהוָה֙ אֵ֣שׁ זָרָ֔ה אֲשֶׁ֧ר לֹ֦א צִוָּ֖ה אֹתָֽם׃ (ב) וַתֵּ֥צֵא אֵ֛שׁ מִלִּפְנֵ֥י יְהוָ֖ה וַתֹּ֣אכַל אוֹתָ֑ם וַיָּמֻ֖תוּ לִפְנֵ֥י יְהוָֽה׃ (ג) וַיֹּ֨אמֶר מֹשֶׁ֜ה אֶֽל־אַהֲרֹ֗ן הוּא֩ אֲשֶׁר־דִּבֶּ֨ר יְהוָ֤ה ׀ לֵאמֹר֙ בִּקְרֹבַ֣י אֶקָּדֵ֔שׁ וְעַל־פְּנֵ֥י כָל־הָעָ֖ם אֶכָּבֵ֑ד וַיִּדֹּ֖ם אַהֲרֹֽן׃
(1) And Nadab and Abihu, the sons of Aaron, took each of them his censer, and put fire therein, and laid incense thereon, and offered strange fire before the LORD, which He had not commanded them. (2) And there came forth fire from before the LORD, and devoured them, and they died before the LORD. (3) Then Moses said unto Aaron: ‘This is it that the LORD spoke, saying: Through them that are nigh unto Me I will be sanctified, and before all the people I will be glorified.’ And Aaron held his peace.
"We are told that Nadav and Avihu offered strange fire. We are not told what it was that made the fire strange. The Hebrew word used here for "strange", zarah, can be translated as "scatter" or "fan". Many commentators have said that these men were trying to do their own thing, and the fire got out of hand. Others say that they were disrespectful toward Aaron and Moses. Still others say that they were drunk. All of these interpretations are possible. [...] I have understood that Nadav and Avihu were trying to get too close to God and when they achieved this, they were burned."
-Rabbi Mark Borovitz, Finding Recovery and Yourself in Torah
Moses' delicate message to the people-and his only consolation to Aaron-is that this was not a random act but a sentence decreed on those closest to God, who are held to the highest standard. What was Aaron's response? Two simple words, וַיִּדֹּ֖ם אַהֲרֹֽן ("And Aaron was silent"). [...] Aaron responded with a profound, shattering silence, a stunning silence, a shocked silence. [...] The deeper human religious response is to be silent, to live with the contradiction, and to affirm that we need not force meaning into tragedy. Sometimes, the deepest response of love is to be silent.
-Blu Greenberg, The Torah: A Women's Commentary