Commento su Levitico 27:26

לא יקדיש איש אתו [ONLY THE FIRSTBORN OF BEASTS…] NO MAN SHALL SANCTIFY IT for the purpose of (to become) a sacrifice of any other description, for it is not his, [being already holy to the Lord from birth] (cf. Arakhin 29a).

ONLY THE FIRSTBORN OF THE BEASTS … NO MAN SHALL SANCTIFY IT — “as a different offering, because it is not his.” Thus the language of Rashi. The correct interpretation is that He is saying: “there is no need to sanctify it [the firstling], for whether it be ox or sheep, it is the Eternal’s automatically.” The verse is thus [to be understood] as a negation.¹⁹³See in Exodus. Vol. II, p. 350, Note 71. And in the Book of Deuteronomy He stated, All the firstling males that are born of thy herd and of thy flock thou shalt sanctify unto the Eternal thy G-d,¹⁹⁴Deuteronomy 15:19. This verse does not mean that the owner is to declare it “holy,” since it is automatically holy by virtue of being the firstborn, but, as Ramban continues, that we are to regard it as holy, etc. meaning that it is holy and that you are to treat it with holiness, so that you are not to do work with it, nor shear it,¹⁹⁴Deuteronomy 15:19. This verse does not mean that the owner is to declare it “holy,” since it is automatically holy by virtue of being the firstborn, but, as Ramban continues, that we are to regard it as holy, etc. and that you are to eat it before the Eternal,¹⁹⁵Ibid., Verse 20. as He will explain.

לא יקדיש איש אותו, no one can declare it as sanctified to be a different category of sacrifice. Seeing it had been born sanctified, the owner cannot change its status.

אך בכור אשר יבוכר לה' בבהמה לא יקדיש אותו, “However, a firstborn that will become a firstling for Hashem among livestock, one must not consecrate;” Rashi understands this to mean that such a firstling as is mentioned in our verse must not be consecrated to be an offering of a different category. [Based on Torat Kohanim, seeing that such a firstling does not belong to the “owner” in the first place.] Nachmanides does not view this verse as a prohibition, but as a reminder that there is no need to consecrate such an animal as the Torah had already conferred the status of “a consecrated” animal on that beast.

אך בכור אשר יבכר לה' בבהמה לא יקדיש איש אותו, “However, a firstborn that will become a firstling for Hashem among livestock, a man shall not sanctify it.” This verse teaches that one must not change the status of animals which have become designated as a specific offering for the altar. For instance, if an animal had been designated to be offered as a burnt-offering, one must not change its status and offer it as a peace-offering. Neither must one (upgrade) an animal designated as a peace-offering to be offered as a sin-offering. This rule applies across the board. Sifra Bechukotai 8,3 adds that from our text I have proof for this rule only if the animal in question had been a frstling, i.e. consecrated from birth. How do we know that this rule also applies to animals which had not been consecrated by birth? We derive this from the extra words לא יקדיש אותו, בבהמה which the Torah wrote in our verse. The word בבהמה in that sequence is not needed and serves as the lesson that no beast which had once been sanctified for the altar may be reclassified.

אם שור אם שה, לה' הוא, “be it ox or sheep, it is the Lord’s.” The original firstborn male animal must be offered, no substitute under any circumstances. (Sifra)