But the firstling of a cow, or the firstling of a sheep, or
 the firstling of a goat, thou shalt not redeem
 That is, shalt not take the redemption price for them, but the creatures themselves; which they, the priests, were to take for their own use: 
 they [are] holy;
 separated to the Lord, and therefore not to be used in common by men, but were sacred to the Lord, or became the property of his priests; see ( Deuteronomy 15:19 ) ; how they were to be made use of follows: 
 thou shalt sprinkle their blood upon the altar;
 for they were to be sacrificed, and their blood used as in other sacrifices: 
 and shalt burn their fat [for] an offering made by fire; for a sweet
 savour unto the Lord;
 as the fat of other sacrifices was, and particularly of the peace offerings, which were wholly eaten otherwise, ( Leviticus 7:31 ) .