What is the significance of the five Shekalim with which the two hundred and seventy-three firstborn redeemed themselves?
Why should the Bechorim pay for losing their Kedushas B'chor?
Oznayim la'Torah (citing the Midrash Rabah): Because the Bechorim who sacrificed to the Golden Calf were Chayav Misah, and earned the right to live either via a Ben Levi or via five Shekalim.
Why don't Levi'im who are born after that time also redeem the Bechoros of Yisrael who are born then?
Da'as Zekenim, Hadar Zekenim and Rosh: Because all future Levi'im descend from Levi'im who already exempted Bechoros, whereas [most] future Bechoros of Yisrael do not descend from Bechoros, and those who do, are not aware of it. 1 Therefore, Hashem decreed that all future Bechoros must be redeemed.
Seforno: Refer to 3:13:2:1.
I do not understand this. Had Hashem decreed that those who descend from Bechoros are exempt, fathers would tell their status to their sons, just like they tell them if they are Kohanim or Levi'im? (PF)