In Parshat Shmini, we are informed of which animals are kosher and which are not.
The explanation of why we are not allowed to eat animals that do not have split hooves and chew their cud is in Vayikra 11:8 “tmeim hem lachem”, “they are ritually impure to you.”
The description of why we don’t eat fish without fins and scales and creatures that creep in the water is because “sheketz hem lachem”, “they are repulsive to you.”
The non-kosher birds are also listed as “repulsive.”
Aside from the descriptions of “ritually impure” and “repulsive”, no actual reason is given for why we are not allowed to eat them and why some animals are ritually unclean or repulsive while others are not. The only thing that we are told is (Vayikra 11:45) “Vehayitem Kedoshim ki Kadosh Ani”, “You shall be holy, for I am holy.”
Commentaries throughout the ages have tried to figure out the reason why God permitted certain animals while forbidding others.
The Rambam (1135-1204), in Moreh Nevuchim explains that pigs are dirty animals, forbidden to be eaten for health reasons.
Sefer HaChinuch, published anonymously in 13th century Spain, adds that even if the harmful character of some of the forbidden foods is unknown to us or to medical science, the True Physician (God) Who admonished us regarding them is wiser. How foolish and rash is he who considers himself as the sole judge of what is beneficial and harmful!
Akedat Yitzchak (1420-1494) explains that the dietary laws are not motivated by therapeutic considerations. If that were so then once the cure for the illnesses caused by eating non-kosher animals would be found people would stop keeping Kosher.
Sefer HaChinuch points out that it is for our benefit that the reasons were not divulged, lest people with scientific pretensions argue: The harm attributed by the Torah to this food only applies to certain types of climates and persons. Some thoughtless people may accept such arguments. To save us from such pitfalls, the reason was not revealed.
Sefer HaChinuch was right. Six hundred years later, the Reform movement’s position was set out in the Pittsburgh Platform of 1885: We hold that all such Mosaic and Rabbinical laws as regulate diet, priestly purity and dress originated in ages and under the influence of ideas altogether foreign to our present mental and spiritual state. They fail to impress the modern Jew with a spirit of priestly holiness; their observance in our days is apt rather to obstruct than to further modern spiritual elevation.
It is interesting to note that over the years many Reform Jews have rejected what was said in the Pittsburgh Platform and have taken on some form of keeping kosher. As well, many Reform Temples have dietary restrictions in their kitchens. In 2010, the laws of keeping kosher were included for the first time in a book put out by the Reform rabbinical association.
The Ramban’s (1194-1270) view is that the laws of kashrut protect our souls. We are forbidden to eat birds of prey lest their bloodthirstiness affect those who eat them.
Abravanel (1437-1508) also believes that the unkosher animals are called ritually impure and repulsive, not poisonous, stressing the spiritual rather than physical source of the prohibition.
We see from here that God intentionally did not give us reasons for why certain animals are kosher while others are not as He didn’t want us to find an excuse to cancel the restrictions.
The bottom line is that we observe the mitzvah of keeping kosher because God commanded us to observe it. Without the Beit HaMikdash, we do not have an obligation to eat meat so those who want to be stringent and choose to be vegetarians are welcome to do so but those who choose to eat meat may not abandon the laws set out for us in the Torah.