במדבר, פרק י״ח, פסוק י״ז

Dedicating the firstborn of pure animals highlights the deep connection between the daily blessings of a household farm and the sacred service of the altar. The holiness of a firstborn is essential and ingrained from its mother's womb, making its sacred status absolute and irreversible. The laws governing these animals apply specifically to the ox, the sheep, and the goat. In this context, the category of sheep includes the animal at any age, rather than being limited to a one-year-old lamb [העמק דבר]. The specific requirements for these animals establish a basic biological rule: the offspring must be the exact same species as its mother. This excludes hybrids or mutations, such as a sheep born to a goat. However, if the offspring possesses even partial physical traits of its mother's species, it retains its obligation as a firstborn, though it is judged as a blemished one [תורה תמימה].

Unlike other sacred dedications that depend on human choice, the holiness of the firstborn exists from birth and cannot be exchanged. It is forbidden to redeem the animal with money to remove its holiness and sell it in a regular meat market, even if it develops a physical blemish [רש״ר הירש]. Any attempt by a person to redeem it is completely invalid, and the animal remains holy [מלבי״ם, שטיינזלץ, רלב״ג]. Nevertheless, because the firstborn is considered the property of the priest, he is permitted to sell it to another person or use it as a betrothal gift, provided the animal maintains its sacred status [תורה תמימה]. The absolute nature of this bodily holiness also extends to other specific offerings, such as the animal tithe and the Passover sacrifice, which share parallel rules with the firstborn [תורה תמימה, חזקוני].

The altar service for the firstborn differs from standard sacrifices. While other offerings require blood to be applied to the four corners of the altar, the blood of the firstborn requires only a single dash against the altar's base [רלב״ג, מלבי״ם, רש״ר הירש]. This single action symbolizes the dedication of the animal's very existence to God, elevating the subsequent eating of its meat into an act of holiness [רש״ר הירש]. Because the laws of the firstborn parallel those of the Passover and tithe offerings, some commentators suggest that the blood of those sacrifices is also dashed from a distance toward the altar. Others disagree, maintaining that the blood of the Passover and tithe offerings is poured from up close directly at the altar's base [תורה תמימה].

Following the application of blood, specific fats must be burned as a fire offering to create a pleasing odor for God. This requirement refers exclusively to the fat that covers the internal organs like a garment or wrapping, a concept supported by ancient linguistic roots that connect the term for fat to clothing and covering [אם למקרא]. This definition deliberately excludes other fats found in the animal's body, such as the fat of the flanks [מלבי״ם]. The offering is not considered fully accepted before God until this specific layer of fat is actually consumed by the altar's fire [צפנת פענח, מלבי״ם]. Ultimately, while the blood and fat are dedicated entirely to the altar and are never eaten [שטיינזלץ], the meat of the firstborn is given to the priests for their own consumption [אבן עזרא, רלב״ג].