Originally, the firstborn sons were to have been the priests of the Jewish nation, who would serve in the Tabernacle and in the Temple and be the spiritual leaders. When G‑d spared the Jewish firstborn during the Plague of the Firstborn in Egypt, He “acquired” them and designated them for this special role.
After the giving of the Torah on Mount Sinai, the Jewish people made and worshipped a golden calf. Click here to read the entire story. The only tribe that did not participate in this shameful act was the tribe of Levi. At this time, the firstborn lost their special status, and it was transferred to the Levites.
In the Torah’s description of the induction of the Levites as they began their new role (Numbers 8:16–18), G‑d tells Moses: “For they [the Levites] are wholly given over to Me from among the children of Israel; instead of those that open the womb all the firstborn of Israel I have taken them for Myself . . .”
May we soon merit seeing the building of the Third Temple, and the return of the Levites to their service.
All the best,
Rochel Chein for Chabad.org