Leviticus 27:26
Only the firstling of the beasts, which should be the LORD’s firstling, no man shall sanctify it; whether it be ox, or sheep: it is the LORD’s. Only the firstling of the beasts, which should be the LORD’s firstling, no man shall sanctify it; whether it be ox, or sheep: it is the LORD’s.
The firstling of ox or sheep already belongs to the Lord by right, so no one may sanctify or consecrate it as a new offering, vow, or dedication as though it belonged to the giver. It is not available to be set apart as a separate or special offering, because it is the Lord's and not the man's to give. A man cannot dispose of what is the Lord's as he chooses or sanctify the firstling for another use. The law distinguishes these clean animal firstborn, which may be offered, from human firstborn and unclean animals, which must be redeemed.
What is vowed to God becomes sacred and cannot be taken for other uses without robbing God. One who wishes to retain vowed property may pay its assessed value plus one-fifth, which makes the vow good while impressing the sacredness of what was consecrated. Giving to God is a duty and not merely something to do when one has money left to spare, since the firstling is not a voluntary dedication. The passage belongs to the presentation of the law of tithing, which asserts that the tithe belongs to the Lord. Civil government has no claim upon it.
The verse illustrates that anathema means something set apart, separated, and devoted. It includes the absolute, irrevocable, and entire separation of a person from the communion of the faithful, from the number of the living, or from the privileges of society. It includes the devoting of any man, animal, city, or thing to be extirpated, destroyed, consumed, and as it were annihilated. Anathema is properly a curse or a ban, something devoted to the Lord for destruction, to be consumed or annihilated.