Leviticus 27:26

Only the firstlings of the beasts,.... These are excepted from being sanctified, or set apart for sacred uses, for a very good reason, suggested in the next clause:

which should be the Lord's firstling, no man shall sanctify it; it being what he has a claim upon, and ordered to be sanctified to him by a law previous to this, Exodus 13:2; wherefore to sanctify such a creature, would be to sanctify what was his before; not merely in a general sense, in which all creatures are his, but in a special sense, having in a peculiar manner required it as his; and therefore to sanctify, or vow to him, what was his before, must be trifling with him, and mocking of him:

whether [it be] ox, or sheep; the firstlings of either of them:

it [is] the Lord's; which he has claimed as his own special and peculiar property, antecedent to any vow of its owner.