A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
lev 27:2CONCERNING VOWS. (Lev. 27:1-18)
When a man shall make a singular vow, &c.--Persons have, at all times and in all places, been accustomed to present votive offerings, either from gratitude for benefits received, or in the event of deliverance from apprehended evil. And Moses was empowered, by divine authority, to prescribe the conditions of this voluntary duty.
the persons shall be for the Lord, &c.--better rendered thus:--"According to thy estimation, the persons shall be for the Lord." Persons might consecrate themselves or their children to the divine service, in some inferior or servile kind of work about the sanctuary (Sa1 3:1). In the event of any change, the persons so devoted had the privilege in their power of redeeming themselves; and this chapter specifies the amount of the redemption money, which the priest had the discretionary power of reducing, as circumstances might seem to require. Those of mature age, between twenty and sixty, being capable of the greatest service, were rated highest; young people, from five till twenty, less, because not so serviceable; infants, though devotable by their parents before birth (Sa1 1:11), could not be offered nor redeemed till a month after birth; old people were valued below the young, but above children; and the poor--in no case freed from payment, in order to prevent the rash formation of vows--were rated according to their means.
lev 27:9if it be a beast, whereof men bring an offering unto the Lord--a clean beast. After it had been vowed, it could neither be employed in common purposes nor exchanged for an equivalent--it must be sacrificed--or if, through some discovered blemish, it was unsuitable for the altar, it might be sold, and the money applied for the sacred service. If an unclean beast--such as an ass or camel, for instance, had been vowed, it was to be appropriated to the use of the priest at the estimated value, or it might be redeemed by the person vowing on payment of that value, and the additional fine of a fifth more.
lev 27:14when a man shall sanctify his house to be holy unto the Lord, &c.--In this case, the house having been valued by the priest and sold, the proceeds of the sale were to be dedicated to the sanctuary. But if the owner wished, on second thought, to redeem it, he might have it by adding a fifth part to the price.
lev 27:16if a man shall sanctify unto the Lord some aprt of a field of his possession, &c.--In the case of acquired property in land, if not redeemed, it returned to the donor at the Jubilee; whereas the part of a hereditary estate, which had been vowed, did not revert to the owner, but remained attached in perpetuity to the sanctuary. The reason for this remarkable difference was to lay every man under an obligation to redeem the property, or stimulate his nearest kinsman to do it, in order to prevent a patrimonial inheritance going out from any family in Israel.
lev 27:26Only the firstling of the beasts--These, in the case of clean beasts, being consecrated to God by a universal and standing law (Exo 13:12; Exo 34:19), could not be devoted; and in that of unclean beasts, were subject to the rule mentioned (Lev 27:11-12).
lev 27:28no devoted thing, that a man shall devote unto the Lord of all that he hath, . . . shall be sold or redeemed--This relates to vows of the most solemn kind--the devotee accompanying his vow with a solemn imprecation on himself not to fail in accomplishing his declared purpose.
lev 27:29shall surely be put to death--This announcement imported not that the person was to be sacrificed or doomed to a violent death; but only that he should remain till death unalterably in the devoted condition. The preceding regulations were evidently designed to prevent rashness in vowing (Ecc 5:4) and to encourage serious and considerate reflection in all matters between God and the soul (Luk 21:4).
lev 27:30all the tithe of the land, whether of the seed of the land--This law gave the sanction of divine authority to an ancient usage (Gen 14:20; Gen 28:22). The whole produce of the land was subjected to the tithe tribute--it was a yearly rent which the Israelites, as tenants, paid to God, the owner of the land, and a thank offering they rendered to Him for the bounties of His providence. (See Pro 3:9; Co1 9:11; Gal 6:6).
lev 27:32whatsoever passeth under the rod, &c.--This alludes to the mode of taking the tithe of cattle, which were made to pass singly through a narrow gateway, where a person with a rod, dipped in ochre, stood, and counting them, marked the back of every tenth beast, whether male or female, sound or unsound.
lev 27:34These are the commandments, &c.--The laws contained in this book, for the most part ceremonial, had an important spiritual bearing, the study of which is highly instructive (Rom 10:4; Heb 4:2; Heb 12:18). They imposed a burdensome yoke (Act 15:10), but yet in the infantine age of the Church formed the necessary discipline of "a schoolmaster to Christ" [Gal 3:24].