Sanctify for Me every firstborn that opens the womb, amongst the Jewish people, both that of man and that of animal — it is Mine(Shemos 13:2). Every firstborn donkey you must redeem with a sheep; if you do not redeem it, you must kill it by striking it behind its neck. And when your son asks you tomorrow, “What is this?” you shall tell him, “With a mighty hand, Hashem took us out of Egypt, from the house of slaves. Pharaoh refused to set us free, so Hashem smote all the firstborns in the Land of Egypt, from the firstborns of humans to the firstborns of animals. I therefore sacrifice to Hashem all the male [pure animals] that open the womb, and all the firstborn of my sons I shall redeem” (v.13-15).

THE MITZVAH

Immediately upon the Jewish people’s departure from Egypt, Hashem commanded them to sanctify both human and animal firstborns. Firstborn sons must be redeemed by giving five (Biblical) shekalim to a Kohen. Firstborn kosher domestic animals are offered in the Beis Hamikdash and eaten by their owners in sanctity. With regard to impure (non-kosher) animals, this mitzvah applies only to the donkey. A person may not make use of the firstborn donkey as long as it is sanctified. He must either redeem it by giving a sheep to a Kohen in its place, or kill it by striking it behind its neck with a kofitz (a type of cleaver), in which case the carcass retains its sanctity and must be buried. Kohanim and Leviim are exempt from this mitzvah.

The Sanctification of Firstborns

The sanctification of firstborns is one of the essential themes of the Exodus. Hashem told Pharaoh that if he refused to allow the Jewish people, whom He called His firstborn, to go free and serve Him, He would take the lives of the Egyptian firstborns instead. Pharaoh refused, and Hashem did as He had promised. At the time that He struck the firstborn humans and animals throughout Egypt, the firstborns of the Jewish people and their animals were in danger of being smitten as well, but Hashem spared them. As a result, the firstborns of the Jewish people became sanctified for Hashem’s service, but that sanctity was lost when the Jewish people sinned with the Golden Calf, and it went instead to the tribe of Levi, who were not involved in that sin (Bamidbar 3:13). We may suggest that firstborns continue to be born with this sanctity, which now belongs to the tribe of Levi, and that is why we must redeem them by giving a Kohen something in exchange.

Sefer HaChinuch (#18) explains that Hashem wants us to remember that all that we accomplish — even after much toil and expense — only reaches fruition because of His assistance and blessings. Therefore, when a person produces his first son, and when his animal produces its first offspring, it is sanctified to Him, and a person takes to heart that everything ultimately belongs to Hashem. In addition, by redeeming our firstborns, we remind ourselves and demonstrate to our children that Hashem freed us from Egypt to serve Him because we are His firstborn.

Additional Reasons: The Firstborn Son

Hashem proclaimed, “You sold Yosef, Rachel’s firstborn, for a profit of five shekalim; you must therefore each redeem your firstborns with five shekalim” (Bamidbar Rabbah 4:10). In addition, when the firstborn of the Jewish people lost their sanctity, its void became occupied withimpurity, and the redemption of the firstborn rectifies this (Avnei Nezer, cited in Shem MiShmuel, Vayakhel 5679). [This would explain why the mitzvah does not apply to Kohanim and Leviim, who did not partake in the sin of the Golden Calf.]

The Firstborn Donkey

On a simple level of understanding, some suggest that this mitzvah applies only to donkeys and not to other impure animals because at the time of the Exodus, donkeys were the only impure animals in the Jewish people’s possession (Hagadas Maasei Hashem). On a deeper level of understanding, the Torah wants to remember how we each emerged from slavery in Egypt with many donkeys laden with jewelry, garments, and other goods (Rashi). The Sages expound that we commemorate the Exodus by redeeming the firstborn donkey upon a sheep because the Egyptians are compared to donkeys, and the Jewish people are compared to sheep, [and the Jewish people attained sanctity through the smiting of the Egyptian firstborn] (Bereishis Rabbah 96:7). One who fails to remove the sanctity from the donkey must instead strike it behind its neck, on the place called the oreph. According to esoteric sources, this is because Pharaoh’s hold over the Jewish people in the spiritual plane is associated with this part of the body. Thus, the word “Pharaoh” is comprised of the same letters as the word oreph (Ohel Moshe, Bechoros, Bei’urim, 1:71).