(2) את הערב this means all kinds of wild beasts, serpents, and scorpions (a mixture [ערב] of noxious creatures) in a crowd (Exodus Rabbah 11:3) — these played havoc with them.
There is a reason given in the Midrash in the case of each plague why this particular one and why that: God came against them with the tactics of warlike operations as carried out by kings in orderly sequence: a government (monarch) who is besieging a city 1) first destroys its water supply, 2) then they blow the trumpets and sound an alarm in order to terrify and dismay them — thus [their water supply was turned into blood], the frogs croaked and made a noise etc. - just as you will find it stated in the Midrash of Rabbi Tanchuma 2:3:4.
LORD is His name! (4) Pharaoh’s chariots and his army
He has cast into the sea;
And the pick of his officers
Are drowned in the Sea of Reeds.
(א) בראשית. אָמַר רַבִּי יִצְחָק לֹֹֹֹֹא הָיָה צָרִיךְ לְהַתְחִיל אֶת הַתּוֹרָה אֶלָּא מֵהַחֹדֶשׁ הַזֶּה לָכֶם, שֶׁהִיא מִצְוָה רִאשׁוֹנָה שֶׁנִּצְטַוּוּ בָּהּ יִשׂרָאֵל, וּמַה טַּעַם פָּתַח בִּבְרֵאשִׁית? מִשׁוּם כֹּחַ מַעֲשָׂיו הִגִּיד לְעַמּוֹ לָתֵת לָהֶם נַחֲלַת גּוֹיִם (תהילים קי"א), שֶׁאִם יֹאמְרוּ אֻמּוֹת הָעוֹלָם לְיִשְׁרָאֵל לִסְטִים אַתֶּם, שֶׁכְּבַשְׁתֶּם אַרְצוֹת שִׁבְעָה גוֹיִם, הֵם אוֹמְרִים לָהֶם כָּל הָאָרֶץ שֶׁל הַקָּבָּ"ה הִיא, הוּא בְרָאָהּ וּנְתָנָהּ לַאֲשֶׁר יָשַׁר בְּעֵינָיו, בִּרְצוֹנוֹ נְתָנָהּ לָהֶם, וּבִרְצוֹנוֹ נְטָלָהּ מֵהֶם וּנְתָנָהּ לָנוּ:
The people then bowed low in homage.
וַיֹּ֨אמֶר מֹשֶׁ֜ה אֶל־הָעָ֗ם זָכ֞וֹר אֶת־הַיּ֤וֹם הַזֶּה֙ אֲשֶׁ֨ר יְצָאתֶ֤ם מִמִּצְרַ֙יִם֙ מִבֵּ֣ית עֲבָדִ֔ים כִּ֚י בְּחֹ֣זֶק יָ֔ד הוֹצִ֧יא ה' אֶתְכֶ֖ם מִזֶּ֑ה וְלֹ֥א יֵאָכֵ֖ל חָמֵֽץ׃
And Moses said to the people,
“Remember this day, on which you went free from Egypt, the house of bondage, how the LORD freed you from it with a mighty hand: no leavened bread shall be eaten.
מִצְוַת עֲשֵׂה שֶׁל תּוֹרָה לְסַפֵּר בְּנִסִּים וְנִפְלָאוֹת שֶׁנַּעֲשׂוּ לַאֲבוֹתֵינוּ בְּמִצְרַיִם בְּלֵיל חֲמִשָּׁה עָשָׂר בְּנִיסָן שֶׁנֶּאֱמַר (שמות יג ג) "זָכוֹר אֶת הַיּוֹם הַזֶּה אֲשֶׁר יְצָאתֶם מִמִּצְרַיִם" כְּמוֹ שֶׁנֶּאֱמַר (שמות כ ח) "זָכוֹר אֶת יוֹם הַשַּׁבָּת". וּמִנַּיִן שֶׁבְּלֵיל חֲמִשָּׁה עָשָׂר תַּלְמוּד לוֹמַר (שמות יג ח) "וְהִגַּדְתָּ לְבִנְךָ בַּיּוֹם הַהוּא לֵאמֹר בַּעֲבוּר זֶה" בְּשָׁעָה שֶׁיֵּשׁ מַצָּה וּמָרוֹר מֻנָּחִים לְפָנֶיךָ. וְאַף עַל פִּי שֶׁאֵין לוֹ בֵּן. אֲפִלּוּ חֲכָמִים גְּדוֹלִים חַיָּבִים לְסַפֵּר בִּיצִיאַת מִצְרִים וְכָל הַמַּאֲרִיךְ בִּדְבָרִים שֶׁאֵרְעוּ וְשֶׁהָיוּ הֲרֵי זֶה מְשֻׁבָּח:
According to a biblical positive command, we must tell on the night preceding the fifteenth day of Nisan all about the miracles and wonders that were performed for our forefathers in Egypt. As it is stated (Exodus 13:3), "Remember this day that you went out of Egypt"; just as it is stated (Exodus 20:8), "Remember the day of the Shabbat." And from where [do we know] that [the remembering] is on the night of the fifteenth? [Hence,] we learn to say (Exodus 13:8), "And you shall recount to your son on that day, saying, 'Because of this'" - at the time that there is matsa and bitter herbs (being 'this') laying in front of you. And [this is the case] even though he does not have a son. Even great scholars are required to tell about the exodus from Egypt. Anyone who relates at length about the events that occurred deserves praise.


