The following section of the Haggadah, taken from the common traditional version, argues strenuously against the intervention of heavenly or human intermediaries in the tenth plague, and possibly in the entire progression of the Exodus:
וַיּוֹצִאֵנוּ ה' מִמִּצְרַיִם. לֹא עַל־יְדֵי מַלְאָךְ, וְלֹא עַל־יְדֵי שָׂרָף, וְלֹא עַל־יְדֵי שָׁלִיחַ, אֶלָּא הַקָּדוֹשׁ בָּרוּךְ הוּא בִּכְבוֹדוֹ וּבְעַצְמוֹ. שֶׁנֶּאֱמַר: וְעָבַרְתִּי בְאֶרֶץ מִצְרַיִם בַּלַּיְלָה הַזֶּה, וְהִכֵּיתִי כָּל־בְּכוֹר בְּאֶרֶץ מִצְרַיִם מֵאָדָם וְעַד בְּהֵמָה, וּבְכָל אֱלֹהֵי מִצְרַיִם אֶעֱשֶׂה שְׁפָטִים. אֲנִי ה'.
"The Lord freed us from Egypt" - not through an angel and not through a seraph and not through a messenger, but directly by the Holy One, blessed be He, Himself, as it is stated (Ex. 12:12); "And I will pass through the Land of Egypt on that night and I will smite every firstborn in the Land of Egypt, from men to animals; and with all the gods of Egypt, I will make judgments, I am the Lord."
In the Yemenite version of the Haggadah, an intriguing addition follows immediately:
Source: פניני משה - הגדה של פסח נוסח תימן - משה קלזן
"Nine thousand myriads" (ninety million) angels descended with God to execute the Egyptian firstborns, but God sidelines them, insisting on carrying out the punishment himself. This late midrashic tradition was apparently popular among Yemenite Jews. A very close parallel can be found in the thirteenth-century Yemenite anthology Midrash Hagadol, where it is placed in the context of the splitting of the Red Sea (Ex. 14:25):
Preserved up to the present time in Yemenite liturgy and lore, the myriads of angels have an antecedent in the (also relatively late) Targum Pseudo-Jonathan (Ex. 12:12).
וְאִתְגְּלֵי בְּאַרְעָא דְמִצְרַיִם בִּשְׁכִינַת יְקָרִי בְּלֵילְיָא הָדֵין וְעִמִּי תִּשְׁעִין אַלְפִין רִבְוָון מַלְאָכִין מְחַבְּלִין וְאֶקְטוֹל כָּל בּוּכְרָא בְּאַרְעָא דְמִצְרַיִם מֵאֱנָשָׁא וְעַד בְּעִירָא
And I will be revealed in the land of Egypt in the majesty of my glory on that night, and with me ninety thousand myriads of destroying angels; and I will slay all the firstborn in the land of Egypt . . .
(In the previous two and other printed sources, the heavenly agents are called "angels of destruction" -- מלאכי חבלה -- or demons, and are numbered at 900, rather than 90, million.)
The tradition to which Pseudo-Jonathan alludes seems to have made its way into the Haggadot of several communities throughout the medieval Jewish world. The twelfth-century French halakhic-liturgical work Mahzor Vitry (p. 293), from the school of Rashi, raises but critiques the practice. The author attests that the Jews of Provence accepted it, while those of Eretz Yisrael did not.* He himself rejects the insertion because it is absent from the Tannaitic Mekhilta (which includes strong parallels to this section of the Haggadah), and due to theological and stylistic objections he has to some of its content:
רַבִּי אֱלִיעֶזֶר אוֹמֵר: מִנַּיִן שֶׁכָּל־מַכָּה וּמַכָּה שֶׁהֵבִיא הַקָּדוֹשׁ בָּרוּךְ הוּא עַל הַמִּצְרִים בְּמִצְרַיִם הָיְתָה שֶׁל אַרְבַּע מַכּוֹת? שֶׁנֶּאֱמַר: יְשַׁלַּח־בָּם חֲרוֹן אַפּוֹ, עֶבְרָה וָזַעַם וְצָרָה, מִשְׁלַחַת מַלְאֲכֵי רָעִים.
Rabbi Eliezer says: How can you know that each and every plague the Holy One brought upon the Egyptians in Egypt was in fact made up of four plagues? For it is said, “His fury was sent down upon them, great anger, rage, and distress, a company of angels of destruction.”
Whatever the reason for the rhetorical campaign against intermediaries, the Haggadah echoes, and amplifies, a tension that already exists within the Torah itself.
In the context of the tenth plague, some verses, spoken in God's voice, emphatically use the singular (Ex. 11:4; 12:12; 12:29), as noted by Mekhilta and our own Haggadah passage. On the other hand, there seems to be a role in the story for a "destroyer" (Ex. 12:13; 12:23). And in Numbers (20:16), there is an explicit reference to a "messenger" who assisted, somehow, in freeing the Israelites.
But our "not through an angel" passage, with its enhanced color in the Yemenite version, takes a strident stance in one direction only. Closely related is the severely diminished role of Moses himself in the Haggadah's narrative. After all, he was God's messenger both to Pharaoh and to the Israelites and should have had a leading place (right after Producer-Director) in the closing credits of the Exodus.
The Haggadah is intent on removing any doubt as to who was responsible for the Exodus. It goes without saying that angels, demons, and human intermediaries have a prominent role throughout the Bible, even with reference to the Exodus. But the Seder night, when we recite and (try our best to) relive our national foundation story, is meant to stand apart. At that time and place, there is no room at the table for angelology, cosmological hierarchies, metaphysical chains of being or, at the opposite extreme, radical materialism. There is only God, Israel, and redemption, both national and personal.
*My thanks to Yehuda Zinberg נ״י for alerting me to Yotzer le-Shabbat Hagadol by R. Joseph ben Samuel Bonfils ("Tov 'Elem," 11th century France), stanza beginning "Kerem Hemed," which refers in verse to the same tradition. See also the commentaries of Pseudo-Rashi, Siddur Rashi, and R. Judah ben Yakar in the Torat Hayyim Haggadah (Jerusalem, 1998), p. 110, and R. Menahem Kasher, Haggadah Sheleimah (Jerusalem, 1967), pp. 186-187.