Another thought on makkat bechorot & pidyon haben

In addition to the excellent points that Rabbi Prince made in his post, I think another way to approach Leah and Aviva's question about makkat bechorot and pidyon haben is that there is a general theme of bechora that runs through the yetziat Mitzrayim story. Before Moshe goes to Mitzrayim to first ask Pharoah to let Bnei Yisrael go, Hashem appears to him and says, "Tell Pharoah, 'So says Hashem: Yisrael is My son, My firstborn. I have told you to send out My son to serve Me, and if you refuse to send him, behold I will kill your firstborn son'" (Shemot 4:22-23). "Bni bechori Yisrael" is the thesis statement of Yetziat Mitzrayim; the purpose of yetziat Mitzrayim is to demonstrate the unique "father/bechor" relationship of Hashem and Bnei Yisrael. The pesukim in perek 4 juxtapose the warning of makkat bechorot with the statement of "bni bechori Yisrael" because the point of makkat bechorot is that it demonstrates the truth of "bni bechori Yisrael." Makkat bechorot indicates to everyone that Yisrael is Hashem's bechor, and since the Mitzriim are torturing His bechor, He strikes their bechorot. Therefore, I think the commemorations of the fact that the Jewish bechorot were saved (pidyon haben, taanit bechorim) are another way of enacting "bni bechori Yisrael"--the Egyptian firstborn were killed, while the Jewish firstborn are consecrated to God.