על נס. עַל כְּלוֹנָס, שֶׁקּוֹרִין פירק"א בְּלַעַז, וְכֵן "וְכַנֵּס עַל הַגִּבְעָה" (ישעיהו ל'), "אָרִים נִסִּי" (שם מ"ט), "שְׂאוּ נֵס" (שם י"ג); וּלְפִי שֶׁהוּא גָּבוֹהַּ לְאוֹת וְלִרְאָיָה, קוֹרְאוֹ נֵס: על נס means [SET IT] UPON A POLE which is termed perche in O. F. Similar is, (Isaiah 30:17) “And like a polo (banner) upon the hill”; (Isaiah 49:22) “I will lift up my pole (banner)”; (Isaiah 13:3) “Lift up a banner." Because it is lofty so that it can serve as a sign and as evidence of something it is called נס, something raised on high (cf. Rashi on Exodus 20:17).
כל הנשוך. אֲפִלּוּ כֶלֶב אוֹ חֲמוֹר נוֹשְׁכוֹ הָיָה נִזּוֹק וּמִתְנַוְּנֶה וְהוֹלֵךְ, אֶלָּא שֶׁנְּשִׁיכַת הַנָּחָשׁ מְמַהֶרֶת לְהָמִית, לְכָךְ נֶאֱמַר כָּאן וְרָאָה אֹתוֹ — רְאִיָּה בְעָלְמָא — וּבִנְשִׁיכַת הַנָּחָשׁ נֶאֱמַר "וְהִבִּיט" — וְהָיָה אִם נָשַׁךְ הַנָּחָשׁ אֶת אִישׁ וְהִבִּיט וְגוֹ' — שֶׁלֹּא הָיָה מְמַהֵר נְשׁוּךְ הַנַּחַשׁ לְהִתְרַפְּאוֹת אֶלָּא אִם כֵּן מַבִּיט בּוֹ בְּכַוָּנָה; וְאָמְרוּ רַבּוֹתֵינוּ וְכִי נָחָשׁ מֵמִית אוֹ מְחַיֶּה? אֶלָּא, בִּזְמַן שֶׁהָיוּ יִשְׂרָאֵל מִסְתַּכְּלִין כְּלַפֵּי מַעְלָה וּמְשַׁעְבְּדִין אֶת לִבָּם לַאֲבִיהֶם שֶׁבַּשָּׁמַיִם הָיוּ מִתְרַפְּאִים, וְאִם לָאו הָיוּ נִמּוֹקִים (ראש השנה כ"ט): כל הנשוך ANYONE THAT IS BITTEN — even though a dog or ass had bitten him, he felt the effects of the injury and became enfeebled more and more (cf. Tanchuma); only that the bite of a serpent kills more speedily. On this account it is stated here: וראה אתו, “whoever has been bitten, when he seeth it, [shall live]” — a mere glance sufficed to heal him. But in the case of the serpent’s bite it is stated והביט, and he gazed — “and it came to pass that if a serpent had bitten any man, when he gazed [at the brazen serpent, he lived]”, for the serpent’s bite was not so quick to heal unless he gazed intently (cf. Jerusalem Talmud Rosh Hashanah 3:9). — Our Rabbis said: But could the copper serpent cause death or life?! But the explanation is that when the Israelites in gazing at the serpent looked up on high and subjected their hearts to their Father in Heaven, they were healed, but if they did not do this they waste away (Rosh Hashanah 29a).