Deuteronomy 14:3

You may not eat of any thing that for you is abominable.

any abominable thing i.e., anything which is abhorrent to a refined spirit, such as the vermin of the earth [cf. comment on Leviticus 18: 22].

THOU SHALT NOT EAT ANY ABOMINABLE THING. He wanted now to add an explanation [to the laws] pertaining to forbidden foods, and therefore he said, Thou shalt not eat an abominable thing, thus declaring that all things that are forbidden are abhorrent to the pure soul, for the meaning of every expression of “abomination” is “hatefulness and repugnance,” similar to, for the king’s word was abominable to Joab; their soul abhorred all manner of food. For forbidden foods that are coarse generate a thickness and obstruction in the soul, as I have explained in its place. Therefore he said further, Of all clean winged things ye may eat in order to declare that [only] those [foods] which He prohibited are “abominable,” and the rest are clean and fit for the pure soul. And in the Sifre the Rabbis have said: 103. “Rabbi Shimon says: Of all clean winged things ye may eat — these are the clean locusts; and all winged swarming things are unclean unto you these are the unclean locusts.” He has said well. Now this is the sense of these verses. He mentioned the prohibition of all winged swarming things, those that go upon all fours, and then he said Of all clean winged things ye may eat to permit those of them which have joined legs above their feet:, Verse 21. the locust, the bald locust, the cricket, and the grasshopper., Verse 22. It was not necessary to explain this because it has already been stated., Verse 22. But he mentioned in general, briefly, Of all clean winged things ye may eat that is to say, all those that have been mentioned are abominable foods, and the rest of the fowls, according their species and multitudes, you may eat of them all clean things which I have not prohibited. Thus he included all things that are forbidden to us, for they are all abominable. It was not necessary afterwards to detail [here] the swarming things and all that creep upon the earth, for it is known that any pure-minded person abhors them completely. But he mentioned the signs of beasts and wild animals, fish, fowl, and carcass [of an animal that died without being properly slaughtered] in order to inform you that they, too, are abominable to the soul. He did not mention treifah since it is not “abominable;” nevertheless, in order to prevent harm to those who would eat it, it is forbidden, because of its poison or mortal sickness. Our Rabbis have yet more interpretations on this …

לא תאכל כל תועבה; before the Torah had been revealed, given, the Israelites as well as mankind generally were aware of the concepts “pure, טהור,” and “טמא, impure.” This is clear already from G’d’s command to Noach to take into the ark with him one pair each of the “impure” species,” and seven pairs each of the “pure” species of animals and birds. (Genesis 7,2) When G’d, after the deluge, permitted man to eat meat, He did not distinguish between meat from “pure” animals and meat from “impure animals.” However, now, after the giving of the Torah, when the Jewish people had become so special, it was no longer appropriate for them to ingest the remains of impure animals or birds (or even fish). Our sustenance should not be dependent on such inferior living beings. We should remain constantly aware of the gulf between man and beast, especially beasts which had never been suitable as sacrifices.