Sforno on Deuteronomy 14:3/ספורנו על דברים י״ד:ג׳

1לא 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.