במדבר, פרק ג׳, פסוק מ״ז

The process of substituting the firstborn Israelites with the Levites resulted in a surplus of firstborns who lacked a matching Levite. To release these remaining individuals from their holy status, God established a personal financial redemption. This payment was specifically collected from the surplus firstborns and not from the Levites [אור החיים]. To fairly determine exactly who would be replaced by a Levite and who would need to pay the money, a lottery was held. Moses prepared slips of paper that read either "Levite" or "five shekels." Any firstborn who drew a slip with "five shekels" was required to pay the fee [תורה תמימה].

This set amount of five shekels became the permanent standard for the commandment of redeeming the firstborn throughout all future generations [חזקוני]. The sum represents the symbolic value of a one-month-old male in relation to the holy [רש״ר הירש, העמק דבר]. Waiting until the child is a month old ensures that the baby is viable and healthy, and the required amount remains exactly five shekels even if the redemption is delayed to a later point in life [העמק דבר]. The payment must be made using a specific holy coin valued at twenty gerahs [ביאור שטיינזלץ]. Using this precise currency is an absolute condition; without it, the redemption does not take effect [אור החיים].

Beyond its economic value, the five-shekel amount holds a deep historical connection to the sale of Joseph. As Rachel's firstborn, Joseph was sold for twenty pieces of silver, which equals the value of one shekel. Because Joseph is historically compared to an ox, and the law for stealing an ox requires a repayment of five cattle, the five-shekel fee serves as a symbolic compensation for the single shekel for which the firstborn was originally sold [ברטנורא].

Why was this financial redemption established as a permanent rule, rather than having future Levites redeem future firstborns? The primary approach among commentators is that there is a fundamental difference in family lineage. All future Levites are direct descendants of the original Levites who already performed the redemption in the desert. However, future firstborns emerge from the entire nation of Israel. Since it is impossible to track which new firstborns descend from those who were already redeemed and which do not, God commanded that from that point forward, every Israelite firstborn must be redeemed with money.