Smith's Bible Dictionary
1. These were things strangled, or
2. dead of themselves or
3. through beasts or birds of prey;
4. whatever beast did not both part the hoof and chew the cud; and
5. certain other smaller animals rated as "creeping things;"
6. certain classes of birds mentioned in Leviticus 11 and Deuteronomy 14 twenty or twenty-one in all;
7. whatever in the waters had not both fins and scales,
8. whatever winged insect had not, besides four legs, the two hindlegs for leaping;
9. besides things offered in sacrifice to idols; and
10. ail blood or whatever contained it (save perhaps the blood of fish, as would appear from that only of beast and bird being forbidden,), Leviticus 7:26, and, therefore,
11. flesh cut from the live animal; as also
12. all fat, at any rate that disposed in masses among the intestines, and probably wherever discernible end separable among the flesh. Leviticus 3:14-17; Leviticus 7:23.
13. The eating of blood was prohibited even to "the stranger that sojourneth among you." Leviticus 17:10; Leviticus 12:14.
As regards blood, the prohibition, indeed, dates from the declaration to Noah against "flesh with the life thereof, which is the blood thereof" in Genesis 9:4, which was perhaps by Moses as still binding upon all Noah's descendants. It is noteworthy that the practical effect of the rule laid down is to exclude all the carnivora among quadrupeds, and, so far as we can interpret the nomenclature, the raptores among birds. They were probably excluded as being not averse to human carcasses, and in most eastern countries, acting as the servitors of the battle-field and the gibbet.
Among fish, those which were allowed contain, unquestionably, the most wholesome varieties, save that they exclude the oyster. Practically, the law left among the allowed Meats, an ample variety.
As Orientals have minds sensitive to teaching by types, there can be little doubt that such mere menial distinctions not only tended to keep Jew and Gentile apart (and so prevented the Jews from becoming contaminated with the idolatry of the Gentiles), but were a perpetual reminder to the former that he and the latter were not on one level before God. Hence, when that ceremony was changed, we find that this was the very symbol selected to instruct St. Peter in the truth that God was not a "respecter of persons."
It remains to mention the sanitary aspect of the case. Swine are said to peculiarly liable to disease in their own bodies. This probably means that they are more easily led than other creatures to the foul feeding which produces it. As regards the animals allowed for food, comparing them with those forbidden, there can be no doubt on which side, the balance of wholesomeness lies.
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Smith, William, Dr. Entry for 'Unclean Meats'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/u/unclean-meats.html. 1901.