In Shemot 12:23, Was הַמַּשְׁחִ֔ית Ha-Mashchit (The-Destroyer) actually HaShem Himself or a Mal’ak?
After reading verse 23 in Exodus 12 :
“For when YHVH goes through to smite the Egyptians, He will see the blood on the lintel and the two doorposts, and YHVH will pass over the door and not let The-Destroyer enter and smite your home.” ( וְעָבַ֣ר יְהוָה֮ לִנְגֹּ֣ף אֶת־מִצְרַיִם֒ וְרָאָ֤ה אֶת־הַדָּם֙ עַל־הַמַּשְׁק֔וֹף וְעַ֖ל שְׁתֵּ֣י הַמְּזוּזֹ֑ת וּפָסַ֤ח יְהוָה֙ עַל־הַפֶּ֔תַח וְלֹ֤א יִתֵּן֙ הַמַּשְׁחִ֔ית לָבֹ֥א אֶל־בָּתֵּיכֶ֖ם לִנְגֹּֽף )
, we may presume הַמַּשְׁחִ֔ית Ha-Mashchit is a different Being separate from HaShem.
However - Commentaries by Chizkuni & Ramban claim Ha-Mashchit was HaShem Himself.
Chizkuni on Shemot 12:23
“and He will not allow the Destroyer to, etc.; ”when our sages in the haggadah said that the line: ועברתי בארץ מצרים, means that G-d personally will carry out the killing of the firstborn, not any category of angel, (compare verse 12) they meant that He would not delegate an angel to perform this task but would perform it Himself, personally.
Ramban on Shemot 12:23
And opportunity will not be given to the Destroyer: The Angel of Destruction in the world at that time, an example, [God] said to the Angel of Destruction, with a might nation you will now deal with by your hand (Shulchan Arukh 24:17) Not [the Angel] of Destruction, rather God, Himself, is the plague.
Based the commentaries of Chizkuni & Ramban, Are we to understand Shemot 12:23 really means “HaShem will pass over the door and not let [Himself] enter and smite your home”?
Was הַמַּשְׁחִ֔ית Ha-Mashchit (The-Destroyer) actually HaShem Himself or a מַלְאַ֤ךְ יְהוָה֙ Mal’ak?
Your fascinating question is addressed in three potential answers here:
Rabbeinu Bachya - it means the angels who are not killing the
firstborn - that was Hashem's exclusive job - but the revenging angels
were killing the evil Jews who were to die that night; the blood on
the door posts will protect the Jews from these punishing angels.
Abarbanel - it means the Egyptian hordes; when the Egyptians see their
children dying, who will protect the Jews from the angry mob? That was
this mashchis who was out that night.
Beis Halevi - the mashchis means
something additional that was a consequence of the killing of the
firstborn. After the deaths of all of these firstborn, a huge plague
broke out - a pollution, a poison entering into and pervading the
atmosphere - there was a horrible mist or fog that was going through
the atmosphere, killing Egyptians. That is why the Jews were
instructed not to go out at night, and Hashem also guaranteed that
this poison won't seep into their homes. The proof is that it says in
Hallel Hagadol, in the above pasuk from Tehillim - Lemake Mitzrayim
Bivchoreyhem - He will smite Egypt through the instrument of their
firstborn; a plague will arise from the bodies of all of these people,
a horrific plague. The Jews will be saved by showing the blood of the
korban pesach, and Hashem will then protect the Jews from all other
aspects of this plague.