A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown [1882] at sacred-texts.com
What man . . . killeth an ox--The Israelites, like other people living in the desert, would not make much use of animal food; and when they did kill a lamb or a kid for food, it would almost always be, as in Abraham's entertainment of the angels [Gen 18:7], an occasion of a feast, to be eaten in company. This was what was done with the peace offerings, and accordingly it is here enacted, that the same course shall be followed in slaughtering the animals as in the case of those offerings, namely, that they should be killed publicly, and after being devoted to God, partaken of by the offerers. This law, it is obvious, could only be observable in the wilderness while the people were encamped within an accessible distance from the tabernacle. The reason for it is to be found in the strong addictedness of the Israelites to idolatry at the time of their departure from Egypt; and as it would have been easy for any by killing an animal to sacrifice privately to a favorite object of worship, a strict prohibition was made against their slaughtering at home. (See on Deu 12:15).
To the end that the children of Israel may bring their sacrifices, which they offer in the open field--"They" is supposed by some commentators to refer to the Egyptians, so that the verse will stand thus: "the children of Israel may bring their sacrifices which they (the Egyptians) offer in the open field." The law is thought to have been directed against those whose Egyptian habits led them to imitate this idolatrous practice.
they shall no more offer their sacrifices unto devils--literally, "goats." The prohibition evidently alludes to the worship of the hirei-footed kind, such as Pan, Faunus, and Saturn, whose recognized symbol was a goat. This was a form of idolatry enthusiastically practised by the Egyptians, particularly in the nome or province of Mendes. Pan was supposed especially to preside over mountainous and desert regions, and it was while they were in the wilderness that the Israelites seem to have been powerfully influenced by a feeling to propitiate this idol. Moreover, the ceremonies observed in this idolatrous worship were extremely licentious and obscene, and the gross impurity of the rites gives great point and significance to the expression of Moses, "they have gone a-whoring."
Whatsoever man . . . offereth . . . And bringeth it not unto the door of the tabernacle--Before the promulgation of the law, men worshipped wherever they pleased or pitched their tents. But after that event the rites of religion could be acceptably performed only at the appointed place of worship. This restriction with respect to place was necessary as a preventive of idolatry; for it prohibited the Israelites, when at a distance, from repairing to the altars of the heathen, which were commonly in groves or fields.
I will even set my face against that soul that eateth blood, and will cut him off from among his people--The face of God is often used in Scripture to denote His anger (Psa 34:16; Rev 6:16; Eze 38:18). The manner in which God's face would be set against such an offender was, that if the crime were public and known, he was condemned to death; if it were secret, vengeance would overtake him. (See on Gen 9:4). But the practice against which the law is here pointed was an idolatrous rite. The Zabians, or worshippers of the heavenly host, were accustomed, in sacrificing animals, to pour out the blood and eat a part of the flesh at the place where the blood was poured out (and sometimes the blood itself) believing that by means of it, friendship, brotherhood, and familiarity were contracted between the worshippers and the deities. They, moreover, supposed that the blood was very beneficial in obtaining for them a vision of the demon during their sleep, and a revelation of future events. The prohibition against eating blood, viewed in the light of this historic commentary and unconnected with the peculiar terms in which it is expressed, seems to have been levelled against idolatrous practices, as is still further evident from Eze 33:25-26; Co1 10:20-21.
the life of the flesh is in the blood: and I have given it to you upon the altar to make an atonement for your souls--God, as the sovereign author and proprietor of nature, reserved the blood to Himself and allowed men only one use of it--in the way of sacrifices.
whatsoever man . . . hunteth--It was customary with heathen sportsmen, when they killed any game or venison, to pour out the blood as a libation to the god of the chase. The Israelites, on the contrary, were enjoined, instead of leaving it exposed, to cover it with dust and, by this means, were effectually debarred from all the superstitious uses to which the heathen applied it.
every soul that eateth that which died of itself (Exo 22:31; Lev 7:24; Act 15:20),
be unclean until the even--that is, from the moment of his discovering his fault until the evening. This law, however, was binding only on an Israelite. (See Deu 14:21).