And Hashem said to Moshe, "Speak to the Kohanim, the sons of Ahron and say to them 'Let no Kohen defile himself through contact with a dead body from his nation'" (VaYikra 21:2)
This passage prohibits a Kohen from becoming defiled through association with a dead body. The only exceptions are the Kohen's closest relatives. The Kohen may care for these departed. The pasuk specifies that the Kohen is prohibited from coming into contact with a dead body from "his nation". What is the meaning of this phrase?
Rashi interprets the phrase to mean that a Kohen can defile himself on behalf of a mait mitzvah a deceased for whom there are no relatives. The obligation to bury this body supercedes the Kohen's prohibition against defilement. The meaning of the pasuk is that the Kohen may not defile himself for a body that is within the nation. The means that the departed is part of the community and will be cared for by relatives. But if the body is outside of the community there are no relatives to care for the body the Priest must bury the body.
Seforno understand the phrase differently. The Kohen cannot defile himself on behalf of a deceased from the general community. However, he does defile himself to care for the body of a close relative.
One very interesting explanation of the phrase is quoted by Mishne Le'Melech in the name of Sefer Yerayim. Mishne Le'Melech explains that the passage specifically excludes the body of an idolater from the prohibition. In other words, the Kohen is not prohibited from contact with the dead body of an idolater. This, of course, raises a disturbing question. The Kohen is not permitted to defile himself. Contact with any dead body even the cadaver of an idolater results in defilement. Why should the prohibition be limited to contact with deceased who are not idolaters?
Mishne Le'Melech proposes an interesting answer to this question. He explains that there are three basic means through which a dead body transmits impurity. The first is though physical contact with the body. If one touches a dead body the impurity is transmitted. The second means is through carrying the body. This means transmits the impurity even without direct contact with the body. The third means is through occupying the same covered area as the cadaver. In other words, through being under a single roof the impurity is transmitted from the body to the person.
Only two of these methods apply to the body of an idolater. This body will transmit though direct contact and through being carried. However, if one is under the same roof as the body, impurity is not transmitted. This suggests that a lesser degree impurity is associated with the body of the idolater. Mishne Le'Melech proposes that the Kohen is not prohibited from contact with this lesser degree of impurity.
Mishne Le'Melech's approach does not seem to completely answer the question. A problem remains unsolved. Assume a Kohen touches the dead body of an idolater. The Kohen will be unclean for seven days. Purification will require sprinkling with the ashes of a red heifer. These consequences are as same as those that occur through contact with the dead body of a Jew. Let us accept Mishne Le'Melech's assertion that the dead body of the idolater does not have the same degree of impurity as the cadaver of a Jew. Nonetheless, the consequences of contact are indistinguishable! Why then, is contact with the idolater's body permitted?
Mishne Le'Melech does not directly answer this question. However, he does provide an interesting hint. He explains that the prohibition against a Kohen defiling himself has a parallel. The Nazir one who makes a Nazerite vow is subject to the same prohibition against defilement. In fact, some of the specific parameters of the Kohen's prohibition are derived from the laws of the Nazir.
This parallel suggests that there is a single consideration underlying the prohibitions upon the Nazir and the Kohen. What is this common denominator? Sefer HaChinuch suggests an explanation for the Kohen's prohibition that can easily be applied to the Nazir as well.
The Chinuch explains that the Kohen is distinguished from the rest of Bnai Yisrael. The Kohen is expected to live a more spiritual life. He is provided with material support through the tithes, the sacrifices and special cities set aside for the Kohanim and Shevet Leyve. These provisions allow the Kohen to disassociate from the mundane and immerse in the spiritual.
The prohibition against contact with the dead is designed to communicate a message. The message is transmitted through symbols. In order to understand the prohibition, we must identify the message and its representation.
Let us begin with the symbolism. The object of the prohibition is the deceased. What does the dead body represent? The human is composed of a material body and a spiritual soul. In death the soul abandons the body. The dead body is the physical element of the human separated from the spiritual soul. In life the human is spiritually clean. With death the body becomes defiled. There is a clear message in this transition. The spiritual soul renders the body sacred. It elevates the material element. Without this spiritual element the material shell looses its sanctity and is reduced to an unclean cadaver. In short, sanctity is derived from the spiritual. The material body, alone, is mundane and impure.
Now we can turn to the message of the prohibition. The restriction against contact with the dead provides an admonishment to the Kohen and Nazir. These individuals are required to live on an elevated spiritual plane. The prohibition against defilement reminds them of their mission. They must concentrate on spiritual development and not be deceived by the allure of the material world. The prohibition communicates this message through symbolically expressing the relative importance of these elements and commanding the Kohen and Nazir to distance themselves from the dead.
Before we can return to the Mishne Le'Melech's comments, we must consider an additional issue. Why is the idolater's body associated with a lower degree of impurity? The insight of the Chinuch provides a response to this question. Defilement represents contrast. When alive, the human possesses a spiritual element. In death, the body is reduced to a purely physical level. The lesser degree of defilement of the idolater extends this symbolism. The idolater failed to adequately develop spiritually. Instead, the idolater brought a material element into the spiritual world. The reduced degree of defilement corresponds with the reduced contrast between life and death.
We can now explain the comments of Mishne Le'Melech. The prohibition against the Kohen's contact with the dead is not dictated by the results of the contact. Contact with the dead body of an idolater has the has the same consequences as contact with the remains of a Jew. Mishne Le'Melech's position is that the prohibition against defilement for the Kohen and the Nazir is symbolic of the mission of these individuals. This symbolism contrasts the spiritual complete human with the material remnant created by death. Only those dead that capture the highest degree of contrast are included in the prohibition. Therefore, idolater's body is not included.
Whether it is a bull, a sheep or a goat, do not slaughter it and its offspring on the same day. (VaYikra 22:28)
This pasuk prohibits the slaughter of a mother and its offspring on a single day. This prohibition applies to slaughtering animals for sacrifice and for personal consumption.
Nachmanides relates this commandment to another mitzvah found in Sefer Devarim. There, the Torah commands us to send away the mother bird from her nest before removing the eggs or offspring. Nachmanides explains that both commandments share a common dual purpose. First, these commandments teach us not to be heartless and cruel. Second, these mitzvot remind us that we are permitted to slaughter animals. However, we cannot destroy the species. Slaughtering the mother and child simultaneously represents disregard for the preservation of the species.
Nachmanides raises an important question. The Talmud teaches that one should not declare that the mercy of the Almighty extends even to the bird's nest. In other words we should not ascribe the mitzvah of sending away the mother bird to the Almighty's mercy. Nachmanides analyzes this teaching. What is wrong with this interpretation of the mitzvah? Why can one not suggest that this is a possible motivation for the commandment? Apparently, the lesson is that we should not ascribe reasons to the commandments. We should regard the mitzvot as decrees from Hashem. We should not attempt to seek rational explanations for the laws of the Torah! Nachmanides acknowledges that this interpretation of the Talmud would render inappropriate his own interpretation of these mitzvot.
Nachmanides explains that he does not intend to dispute the position of the Talmud. Instead, he explains that the Talmud's admonishment must be more carefully considered. He asserts that the Sages never intended to discourage interpretation of the commandments. According to the Sages, King Shlomo interpreted virtually all of the mitzvot. There is no indication that he acted improperly. The Sages were explaining that a specific type of interpretation is inappropriate.
Nachmanides explains that all mitzvot are given to benefit humanity. Mitzvot do not benefit the Almighty. Hashem is perfect and complete. He is does not derive any benefit from our performance of the mitzvot. Neither is He harmed by our transgression. Therefore, we cannot assert that Hashem's mercy extends to the bird's nest. Such an assertion would result in a series of false conclusions. First, it would imply that the Almighty feels mercy for the bird. Second, in order to respond to this feeling He commands us to send away the mother. Third, the Almighty's sense of mercy will be frustrated by our neglect of the commandment. All of these implications are false.
Instead, these mitzvot are designed to make us better individuals. We learn mercy and compassion from the commandments. Similarly we acquire other positive traits through the observance of the other mitzvot.
 Rabbaynu Shlomo ben Yitzchak (Rashi), Commentary on Sefer VaYikra 21:1.
 Rabbaynu Ovadia Sforno, Commentary on Sefer VaYikra 21:1.
 Rav Yehudah Rosanes, Mishne Le'Melech, Hilchot Avel, 3:1.
 Rav Yehudah Rosanes, Mishne Le'Melech, Hilchot Avel, 3:1.
 Rav Ahron HaLeyve, Sefer HaChinuch, Mitzvah 263.
 Mesechet Berachot 33b.
 Midrash Rabba, Sefer BeMidbar 19:3.
 Rabbaynu Moshe ben Nachman (Ramban / Nachmanides), Commentary on Sefer Devarim 22:6.