In the Bible, G‑d lists two requirements for an animal to be kosher (fit to eat) for a Jew: Animals must chew their cud and have split hooves. Pigs do have split hooves but do not chew their cud, so we cannot eat pig meat and its derivatives. In the seafood department, we may only eat fish that have both fins and scales.
Here is a translation of the original Divine command, from Deuteronomy, Chapter 14:8-10:
And the pig, because it has a split hoof, but does not chew the cud; it is unclean for you. You shall neither eat of their flesh nor touch their carcass.
These you may eat of all that are in the waters; all that have fins and scales, you may eat.
But whatever does not have fins and scales, you shall not eat; it is unclean for you.
While the commandment to follow a kosher diet falls under the category of laws which do not necessarily seem logical,1 observing them only because G‑d commands us to,2 there are moral lessons we derive from them.
Here are several given:
The birds and many of the mammals we do not eat are predators, while the permitted animals are not. We are