They are holy Namely, in a peculiar manner, consecrated to a holy use, even to be sacrificed to God, Deuteronomy 15:19. The flesh All the flesh of them, and not only some parts, as in other sacrifices.
Related Commentaries of Numbers 18:17
Numbers 18:17-18
17 But the firstling of a cow, or the firstling of a sheep, or the firstling of a goat, thou shalt not redeem; they are holy: thou shalt sprinkle their blood upon the altar, and shalt burn their fat for an offering made by fire, for a sweet savour unto the LORD.
18 And the flesh of them shall be thine, as the wave breast and as the right shoulder are thine.