What do all the forbidden animals have in common, that explains why the Torah forbids them specifically?
Ramban #1: Refer to 11:13:4:1***.
Ramban #2 and Seforno: The Torah forbids the animals, the beasts, the birds, the fish, the species of locusts and the vermin that it does, because they are harmful to the body 1 and cause it to become hot.
Kolbo 101, also in Orchos Chayim 103: The Kosher animals are herbivores. They do not have top teeth. They cannot properly grind their food while eating, due to fear of predators or other reasons. Rather, after minimal chewing, the food goes to a stomach, and later it regurgitates it and grinds it. Split hooves show that it does not poison or tear (other animals). Food converts the nature of the eater to be like what he eats.
Akeidas Yitzchak (Sha'ar 60): Not chewing the cud hints that it is always hungry and not satisfied with the food in its innards. Long toenails are to steal [from other animals]. Eating such animals leads to such Midos in the eater.
Shlah ha'Kadosh (17, and Hagahah): Chewing the cud shows that it is satisfied with what is in it. Split hooves shows that it is not Dores. The Neshamah is weakened if the body is filthy 2 .
Why does the Pasuk find it necessary to single out the camel, the rabbit, the hare and the pig, seeing as all animals that do not possess the two above-mentioned Simanim are not Tahor?
Ramban (on Pasuk 3): To teach us that they are the only animals in the world that possess only one of the two Simanei Taharah.
Why did the Torah need to say "Ach Es Zeh Lo Sochlu mi'Ma'alei ha'Gerah umi'Mafrisei ha'Parsah"? It said above "Zeh ha'Chayah Asher Tochlu"! R. Chanina ben Gamliel (Kidushin 61a) holds that from positive, we infer negative!
Targum Yonasan, Bechoros 6a: To include in the prohibition an animal whose mother is a Tamei animal, even though it (the baby) possesses both Simanei Taharah. 1
See Peirush Yonasan.
Why does the Pasuk not insert here the Din of Tum'ah of animals that walk on the soles of their feet (and not on hoofs - such as dogs, bears and cats), as it does later in Pasuk 27 regarding Tum'ah?
Ramban (Pasuk 24): Because the Pasuk here is discussing the prohibition against eating, and it is uncommon to eat them. 1
R. Avahu (Pesachim 21b) holds that whenever the Torah says "Lo Sochal", even benefit is forbidden. Why do we benefit from pig lard?
Moshav Zekenim: R. Avahu discusses matters proper to eat; this lard is not proper to eat. This is why we may ride on horses 1 and benefit from rabbit hides. We anoint with Chelev of Tamei animals, for Refu'ah is permitted; we are lenient about Safek mortal danger. 2
Moshav Zekenim (13): "Lachem" 3 permits benefit.
Panim Yafos: Tamei species, even if they are slaughtered, are Neveilos. The Torah permitted benefit from Neveilos. 4
Is there no other source to permit benefit from Tamei animals?! We need verses to forbid camel's milk, and eggs of Tamei birds (refer to 11:4:152:1, 11:17:151:1)! An animal traded for a dog is Pasul for a Korban (Devarim 23:19). This implies that a dog has value! There a Mitzvah to help others unload and load donkeys (Shemos 23:5, Devarim 22:4), donkeys taken from Midyan were shared with Yisrael, Leviyim and Elazar (Bamidbar 31:39,47), we redeem a firstborn donkey (Shemos 13:13); Yakov blessed with Ru'ach ha'Kodesh that in Yehudah, they will use donkeys for harvesting (Bereishis 49:11); it is difficult to say that the Isurim to plow with an ox and donkey together, and for a king to acquire excess horses (Devarim 22:10, 17:16) are merely extra Lavim, for no one may benefit from a Tamei animal. - PF)
If so, it is permitted only if there is mortal danger! (PF) Moshav Zekenim adds that this is the Heter to fast on Shabbos due to a bad dream; if not, perhaps he will die! We do not act based on dreams, but most are fulfilled, like those of Pharaoh and Nebuchadnetzar,
It says "Lachem" regarding Tamei species of animals, fish, Sheretz ha'Of, Chagavim, and Sheratzim (verses 4-8, 10, 12, 20, 23, 26-27, 31. - PF)
This does not apply to live animals, Perhaps he holds that the Isur Achilah was taught about dead animals, so we infer an Isur Hana'ah only for dead animals. (PF)
What do we learn from "Es ha'Gamal"?
R. Shimon (Bechoros 6b): This forbid camel's milk. 1
Rashi (26) writes that a camel's hooves are split above, but not below. If so, why does the Torah say "u'Farsah Einenu Mafris"? It should say "v'Shesa Einenu Shose'a"!
Gur Aryeh: The Torah means that it is not Mafris Parsah totally.