Traditional Jews keep kosher. The laws of kashrut begin in the Torah. God instructs: Do not “boil a kid in its mother’s milk” (Exodus 23:19, Exodus 34:26 and Deuteronomy 14:21).
God gives signs to determine if an animal is kosher or not. All kosher animals must have split hooves and chew their own cuds.
Having just one of these signs (like a pig, which has split hooves but doesn’t ruminate) is not sufficient. The preferences of some delis and caterers aside, there is no category in Jewish law called “kosher-style.”
Many reasons for keeping kosher have been cited. They include health or environmental considerations, but for traditional Jews these are not the main reasons. For them, one eats kosher because the Torah says to do it; we don’t understand why, but show obedience to God by eating kosher.
As later developed, the laws of kashrut are extensive. They include prohibitions against eating certain animals; require that permitted animals be killed by shechita, ritual slaughter, and the animal’s blood drained or broiled out; that fruits and vegetables are checked for bugs; that meat and dairy not be eaten together; and that grape products prepared by non-Jews are not eaten at all.
Keeping kosher, however, does not have to be hard. If you don’t keep kosher and are interested in doing so, consult your favorite rabbi.