To an observant Jew, the laws of kashrus (kosher) are many and sometimes complex. In spite of their complexity, they serve a purpose. In This Is My God, author Herman Wouk points out that the purpose is not medical, contrary to some opinions. Some assume, for instance, that the prohibition against eating pork was because of the diseases that improperly cooked pork could cause. If that were the reason not to eat pork or horse, then the law could simply have required all meats be thoroughly cooked. Rather, Wouk says, the kosher laws were to set the Jewish people apart from their neighbors. Some of the laws have no health component, or any other logical reason for existence, but keeping them shows devotion to the Law.
Many of the laws about what could or could not be eaten, about how to prepare food, and about eating utensils, are clearly spelled out in the Law of Moses. For instance, Leviticus 11 goes into great detail about which animals are “clean” and “unclean.” That same chapter goes into the purification of vessels that have touched something unclean, but it further modified by Numbers 31:21-23.
As detailed as some of these laws are, over time situations came up that had no clear scriptural answer. Sometimes the interpretation can be explained, but is clearly designed as a hedge to keep from violating another law. Such is the requirement that one not eat dairy products and meat in the same meal (sorry, no cheeseburgers or sausage pizza with cheese). The justification for this requirement is, “Thou shalt not seethe a kid in his mother's milk.” (Deut 14:21) Some would ask how you get from there to not mixing any dairy with any meat. The answer is that such a requirement was made to avoid any possibility of the dairy product being from the mother of the meat product. Of course, that would not explain not eating dairy with chicken or fish. Technically, that would not even explain prohibiting beef and dairy, since that law specifies goat meat. To further complicate matters, the interpretation includes time frames. One may not eat a dairy meal (or even a candy bar) within six hours, in most traditions, of a meat meal. One can eat meat immediately after rinsing the mouth and hands after a dairy meal, as long as they are not part of the same meal.
Some rabbis aver that the laws of kashrus applied from the beginning (or at least from the flood) and predate the giving of the Law on Sinai. Those scholars, however, have a difficult time proving that in the case of dairy and meat. Abraham was talking to God and saw some travelers coming. He offered his hospitality to the men. “And he took butter, and milk, and the calf which he had dressed, and set it before them; and he stood by them under the tree, and they did eat.” (Gen 18:8) Clearly Abraham did not know that he could not serve meat and dairy together. Equally clearly, the laws of kashrus applied specifically to the Jewish people after the exodus from Egypt.
Some Christians insist on keeping kosher. Generally this is attributed to the Seventh Day Adventists, but the truth is that a significant portion of Adventists prohibit eating any meat. Some do allow dairy and eggs, while others are strict vegetarians. Some seem to emphasize the prohibition of pork, but say little, if anything, about the other restricted animals. Most try to justify their position by quoting health issues, even though (as has been seen) the restrictions were not primarily medical. Some of these Christians are put into seemingly contradictory positions. The kosher laws (which all relate, incidentally, to animal flesh) would be part of what they call the Ceremonial Law (as opposed to the Moral Law in the Ten Commandments), which they feel they are not obligated to obey, and yet they try to force it on others.
Kashrus may have some health benefits. Its most significant benefit, though, is to establish a separation between the Jewish people and the gentiles. There is absolutely nothing wrong with keeping those laws, and even the rabbinic interpretations. As with circumcision, however, requiring it for those to whom the laws were never given becomes unnecessarily divisive. Paul points us back to Abraham (Galatians and Romans), and Abraham did not keep kosher as it is defined today.