The Haggadah Yad Mitzrayim by the Gaon R’ Yitzchak Isaac Chaver raises a wonderful question. In Dayeinu we say: If He had brought us out of Egypt and not executed judgments upon them – it would have been enough for us; If He had executed judgments upon them, and not upon their gods – it would have been enough for us; If He had executed judgments upon their gods, and not slain their firstborn – it would have been enough for us.
R' Chaver asks, if we mention executing judgments upon the Egyptians, does this not include Makat Bechorot? Why do we need to mention Makat Bechorot separately again?
The Mishna Berurah writes (66:53): The Tur writes in the name of the Yerushalmi: One must truly mention and establish the exodus from Egypt, the kingship [of G-d], the splitting of Yam Suf, and the plague of the firstborn.
And thus, we recite in Shacharit: True, from Egypt You redeemed us, Hashem our G-d, from the house of bondage You liberated us, all their firstborn You slew, and Your firstborn Yisrael You redeemed, and the Red Sea You split for them.
And in Maariv we say even more: Who struck in His wrath all the firstborn of Egypt and brought out His people Yisrael from among them to eternal freedom.
So, we don't mention the plagues of blood or frogs or boils or any other; just Makat Bechorot, and twice each day. The question is: why is that?
Another question that needs clarification: It is known that in Makat Bechorot there were no partners – not Moshe and not Aharon and not the ministering angels, but only Hakadosh Baruch Hu, in His glory and by Himself, and thus we say on the Seder night: And Hashem brought us out of Egypt – not through an angel and not through a seraph and not through a messenger, but Hakadosh Baruch Hu in His glory and by Himself. As it is stated, 'And I will pass through the land of Egypt on this night, and I will strike every firstborn in the land of Egypt, from man to beast, and upon all the gods of Egypt I will execute judgments, I am Hashem.' And I will pass through the land of Egypt – I and not an angel. And I will strike every firstborn – I and not a seraph. And upon all the gods of Egypt I will execute judgments – I and not a messenger. I am Hashem – I am He and no other
