Based on a shiur on Tisha B'Av heard from Rav Aryeh Leib Shapiro shlit"a, Menahel Ruchani of Yeshivas Ponovezh l'Tz'irim (any errors are the writer's alone)
Parshas Re'eh reviews the kosher species in the animal, bird, fish, and insect kingdoms. Greater specifics are given for the kosher animals detailing the ten species of kosher domesticated and non-domesticated animals. The Torah restates the two kosher signs for animals: cleft-hooves and regurgitation and re-swallowing of food, or the "cud".
Vilna Gaon notes that one kosher sign, the split hooves, is external, and one kosher sign, the "chewing of the cud", is internal. Cleft-hooves, the external sign, are only suitable for walking, not hunting, not kicking, just walking. Chewing the cud, the internal sign, indicates that the animal eats according to its needs and chews and chews until every last bit of nutrition is extracted from the cud. In other words, that animal acts in a non-aggressive, non-desirous manner. Ramban (Shmini) explains that Hashem only permitted those animals which exhibit "good middos" not the aggressive, desirous animals of prey whose consumption would spiritually implant within us similar qualities.
The Gaon further elaborates based on the Midrashim which compare the four malchiyout to the four animals which bear only one kosher sign. Bavel, Yavan, and Madai are parallel to the gamal, the arneves and the shafan which have the internal kosher sign but not the external one. Edom is parallel to the chazir which possesses the external kosher sign but not the internal one. A famous teaching compares Edom/Eisav to the chazir who proudly displays the external kosher sign in attempting to lure the Jewish people to follow its ways. The first three kingdoms, although displaying intense wickedness, had certain internal redeeming qualities. Edom was the opposite. Outwardly, they appeared cultured but were internally morally corrupt. A frightening parallel existed in the inheritors of the Edomite kingdom, the German Third Reich and the Nazi hordes and their helpers whose outward "culture" was world famous but whose inner moral depravity surfaced in the Holocaust.
The Talmud (Yerushalmi Yoma 1:1, 4b and Bavli Yoma 9b) states that the first Beit HaMikdash was destroyed because of the violation of the three cardinal sins of arayos, avoda zara, and murder. But yet, since their sins were revealed, their time for redemption was revealed as well - exactly 70 years, after which the exile ended. By contrast, during the period of the second Beit HaMikdash, the people, notes the Yerushalmi, "toiled in Torah and were meticulous in mitzvos." Why, then, was the second Beit HaMikdash destroyed? The Yerushalmi answers that "they loved money and hated one another" in contrast to the period of the first Beit HaMikdash whose people "relied on G-d" (Bavli Yoma 9b). Similarly, the Midrash notes that even the idolatrous Achav was victorious in battle since the Jews treated each other lovingly. Since the sin of the Jews of the second Beit HaMikdash was not revealed, the end of their exile was not revealed. (See Bavli Yoma 9b; the Yerushalmi seems to have a different version of this statement).
How can it be stated that the Jews during the first Temple period "relied on G-d"? To worship idols? To commit incest and adultery? Furthermore, what does the Gemara mean that the sin of the Jews during the second Temple period was not revealed? The Yerushalmi and Bavli reveal it as baseless hatred!
The Gra explains that the nature of the sins was very different. The yeitzer hara for arayos and avoda zara was supernaturally great during the first Temple period. The Gemara in Sanhedrin even records that the Anshei Knesset HaG'dola prayed for the elimination of the yeitzer hara for idolatry and the lessening of the yeitzer hara for arayot. Internally, though, we are taught, regarding their middos, they "relied on Hashem." This is what the Yerushalmi means by stating that "their sin was revealed," meaning, internally, their character traits were basically good, but externally their conduct was despicable. By contrast, the people of the second Beit HaMikdash acted in exactly the opposite way. Externally, their conduct, at least bein adam laMakom, was perfect; they were "z'hirin b'mitzvos", but, internally, their middos were highly deficient, which expressed itself in terrible conduct bein adam lachaveiro. "They loved money, and hated each other."[1] Their sin was not revealed, meaning, the source of their sins was their internal defective middos. Outwardly, they seemed to be acting properly. For this reason, the Gemara (Yoma ibid.) concludes: "better is the fingernail of the earlier ones than the stomach of the later ones." According to the Gaon, this is not just a statement comparing a smaller part with a larger part of the anatomy. The nail is a revealed part of the body; this is parallel to the kosher sign of split hooves. The stomach is hidden; this is parallel to the kosher sign of chewing the cud. The Gemara is telling us that the outward conduct of the Jews during the first Beit HaMikdash, although sinful, was better than the inner, rotten middos of the Jews during the second Beit HaMikdash.
This duality of internal middos and external action is a central theme in avodas Hashem. Indeed, the Torah "summarizes" what is expected of us as servants of G-d in a verse in Parshat Eikev, made famous by the Mesillas Yesharim: "What does G-d ask of you, but to fear Hashem, to walk in His ways, to love Him, to serve Him wholeheartedly, and to keep all of His mitzvos..." Four out of the five directives focus on internal middos, emotions, or thoughts; only one addresses "keeping all of the mitzvos." Of course, perfect middos alone, not translated into action both in keeping the bein adam laMakom and mitzvos bein adam lachaveiro, are suspect and incomplete. But, if the actions are solely external with corrupt or even imperfect middos, then these middos will serve as the primary cause of much sin.
We have past the somber period of the Three Weeks, the mournful climax of Tisha B'av, the redemptive holiday of Tu B'Av, and are now reading the seven prophecies of consolation leading us through the month of Repentance of Elul and the days of Din v'Rachamim of Rosh HaShana and Yom Kippur. Let us all incorporate within ourselves the message of the destruction of both of the Batei Mikdash underscoring the utter centrality of both the external observance of mitzvos, but, even more importantly, the development of proper middos. Of course there is a symbiosis between the two. As Seifer HaChinuch writes often: "after the actions go the thoughts." Proper middos are not developed in a vacuum. They are fostered by actions expressing those middos (see Michtav Mei'Eliyahu by Rav Dessler, Kuntres HaChessed for example) and by learning about the centrality of being samei'ach b'chelko and avoiding excess, of avoiding jealousy, of soft-spoken speech and soft rebuke, of concern for other's property and feelings. May we merit teshuva sh'leima and the return of the Beit HaMikdash.
[1] Noam Elimelech explains that as a result of the Anshei Knesses HaGedola's prayer, the irrational desire for idolatry was converted to an irrational desire for money!