The Tenth Plague is Central to the Exodus

The Tenth Plague is Central

ואגב יש לומר ג"כ הטעם דעיקר גאולת מצרים דווקא ע"י מכת בכורות וגם כי התחלת ההתראות היה במכת בכורות מפני דידוע דתכלית גאולת מצרים היתה כדי להודיעו ולפרסם ע"י כן את כל העולם האחדות ב"ה וב"ש. והנה מצרים לאשר שטופים בע''ז היו, ובוודאי הקטן אי אפשר לו להתפאר לגדול הימנו שהוא אלקה, מפני שהגדול ממנו יודע וראה בעיניו שילוד אשה הוא נולד מטפה סרוחה מבשר ודם משא"כ הגדולים הזקנים באים להונות את הקטנים ואת נעריהם בטחי תפל ומדוחי שוא ושקר שהמה אלקות והם עצמם בראו את עצמם כמו שאמר פרעה שהוא ברא את עצמו ועשה את עצמו לאלקות כדאיתא במדרש. ע''כ הכה את הבכורות אפילו בכור הבית הכה כמו שהמה בעצמם יודו שאין אלקה רק אלקי ישראל ביה וב"ש הגדול. וכדאיתא בגמרא כשהקב"ה נפרע מן האומה נפרע מאלהיה עיין רש"י בא י"א ה'.

The redemption from Egypt was fulfilled through the plague of the first born; this was also the first warning that God gave to the Egyptians. (See Ex. 4:22-24, "Thus says the Lord: 'Israel is my first born. I have said to you, Let My son go that they may worship Me; Yet you refuse to let them go. Now I will kill your first born.'") The reason for this is that the purpose of the redemption from Egypt was to make known and publicize the power and unity of God in the world. (This could only be accomplished by striking down the first born.) Egypt was mired in idolatry, the oldest Egyptians claiming they were gods. As a result, Egyptians who were younger could never boast to those who were older than them they were gods. Their elders had witnessed with their own eyes that they were born of a mortal women from a putrid drop of semen. The elders, on the other hand, could deceive those who were younger as well as their own children with false oaths and lies claiming that they were gods and that they had created themselves, just as Pharaoh said about himself. Therefore, when God struck down the first born, even the firstborn of every household, they had to admit that there is no God but the God of Israel, blessed be God's name. This is stated in the Talmud: When the holy one took vengeance on the whole nation and punished its gods. (See Rashi, Ex. 11:5)[1]

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[1] The Torah states in Exodus 11:5,  "Every firstborn in the land of Egypt will die, from the firstborn of Pharaoh who sits on his throne to the firstborn of the slave woman who is behind the millstones, and every firstborn animal." Rashi wonders why it was necessary to cause suffering to  the other slaves in Egypt. He offers two answers: first, the non-Israelite slaves were guilty of oppressing the Israelites; and second, by striking all the first born, it became clear that the first born were not gods and only the God of Israel could punish them.