Of all the regulations given in Leviticus, perhaps the most incomprehensible is the prohibition against wearing garments made from different materials (Leviticus 19:19). Also in this verse are commands against cross-breeding animals and sowing a field with a mixture of seeds. But at least these other regulations seem to have a semblance of common sense to them, as does Deuteronomy 22:10 with its prohibition against plowing a field with a team consisting of an ass and an ox.
It turns out that Leviticus 19:19 is just a small part of a whole complex of ideas that begins in Genesis and ends in Revelation. So below is a rough summary of the overarching concepts holding them all together.
Proper Borders
One of the first things we learn about God in Genesis 1 besides His creative acts is that He is a God of order, with everything in its proper place. God begins by creating certain realms formed by acts of divine separation: light from dark, atmosphere from earth, and water from dry land. Then each of these realms was populated by appropriate things or beings especially suited to their individual environments. Whether one understands Genesis 1 as a scientifically accurate account or divine mythology, the fact remains that these actions of God are definitely accompanied by theological insights into the nature of God.
Concerning the original separation acts, limits are set for the water. As it says poetically in Job 38:8-11: “God set bars and doors and pronounced, 'You shall go so far and no further, and here your proud waves with stay.'” These limits set for the water are only transgressed once in the OT, and that is of course when God allowed the water to flood the earth and cleanse it of all the evil present there. Interestingly, one of the possible precipitating factors bringing about the Flood is the prohibited interbreeding described rather obscurely in Genesis 6:1-4 between the sons of God and the daughters of men. There are various interpretations of what that really means (see my post on that passage), but in any case, it definitely represented a prohibited form of mixing what should not have been mixed.
We then read further in Genesis that after the Flood came the incident of the Tower of Babel resulting in God scattering the people throughout the earth. Paul may have been referring to that event when, in Acts 17:26, he tells the inhabitants of Athens that God “allotted the boundaries of their existence.” It is interesting that one of the few ecclesiastical groups in recent times to make a major issue out of this verse is the Dutch Reformed Church. It quoted this passage in a 1976 document defending the policy of apartheid in South Africa on biblical grounds. Of course, the rank hypocrisy of such an interpretation is exposed by the fact that it was the Dutch in the first place who colonized lands “allotted” to the African tribes inhabiting that land. This church body recanted their position ten years later. For a little more on this issue, see my post titled “Apartheid in the Bible?”
Again, assuming that Paul was citing aftermath of the Babel event, the following verse, 17:27, explains God's rationale for dividing up mankind into different geographical regions when he says, “so that they would search for God and perhaps grope for him and find him – though indeed he is not far from each one of us.” (NRSV) If so, then this passage in Acts thoroughly discredits Michael Heiser's repeated assertion in his writings that God was punishing the people at Babel by disbursing them, and basically washing His hands of all non-Jews at that time.
This OT theme of dividing people groups geographically and linguistically takes a complete U-turn in the New Testament beginning at the Day of Pentacost when there is a symbolic reversal of multiple languages now becoming one spiritual language that all can comprehend. That reversal is continued during the ministry of the early church beyond the bounds of Israel to encompass an Ethiopian, Samaritans, and pagans living throughout the Roman Empire. Paul stresses that in Christ there is neither Jew or Greek, slave or free, male or female (Galatians 3:28; Colossians 3:11). And it culminates in the Book of Revelation with its seven-fold repetition of the saved of “every people, every tongue, every tribe, etc.”
Getting back to the original separations made by God and described in Genesis 1, that theme also reaches its conclusion in Revelation, where we learn that the moon will become blood and the stars will fall from the sky (6:12), there will be no more sea (21:1), heaven will come down to earth (21:2), and there will be no more night or sun (22:5). At that point in time, there will no longer be the need for any such physical boundaries since all will be incorporated together in the New Heaven and New Earth under the eternal reign of God.
Another aspect of the theme of proper boundaries is seen in man's repeated attempts to transgress the limits set for him. We see this first in Adam and Eve's attempt to be like God Himself, followed later by the building of the Tower of Babel in trying to reach heaven when God had told them to disburse throughout the earth instead. The theme continues as Job and his friends try to figure out God's secrets when they don't even yet understand the secrets of the physical world around them, as God points out in a series of questions addressed to Job in chapters 38-41.
Again, this particular aspect of proper boundaries reaches its conclusion with another reversal. Instead of mankind ascending to heaven at last, it is actually God who transcends boundaries by descending to earth from heaven (Revelation 21-22).
Clean and Unclean Animals
Taking these original creations one step further, the animals dwelling in the three realms described in Genesis 1 are then described in more detail in the regulations in Deuteronomy 14:2-20 concerning which are ritually clean animals suitable for food and which are unclean ones. The reason behind these regulations is given at the start of that chapter – “For you are a people holy to the LORD your God.” – as well as in verses 9-11. The rationale behind the particular divisions of animals has been explained as due to hygienic reasons, avoidance of pagan worship rituals of the time, or as a totally arbitrary set of criteria chosen by God to test the people's obedience and form a division between them and all surrounding cultures.
I think the rationale goes way beyond all of those explanations, as hinted at in Deuteronomy 14:1 quoted above. Levinson give the reason succinctly: “Animals that do not satisfy the defining characteristics for their group are not to be eaten.” Thus, for example, birds are clean as long as they can fly, are active in the daytime, and eat nothing other than plants and invertebrates. All others fall outside the ideal type for air dwellers. Similar restrictions are laid down for the fish and land creatures.
It is not hard to imagine which of the two categories the ancient Jews would have assigned for the platypus, the epitome of an animal which has characteristics found in a number of different species.
This points to another related sub-theme found throughout the Bible where fantastic creatures are described. A tracing of that theme is found in the post “Monsters in the Bible.”
Deuteronomy 22:5 is a command against cross-dressing. Deuteronomy 22:9 contains the same restriction against mixing seeds as in Leviticus 19:19, and Numbers 15:37-40 is another passage concerning the mixing of different materials together in a garment. D.P. Wright says, “One reason mixtures are prohibited is that such prohibitions are reminders that the people, keeping themselves distinct, are holy.” And Levinson says that “these laws attempt to maintain specific boundaries between categories seen as incompatible...”
This theme of clean and unclean pops up again in the New Testament. Self-righteous groups such as the Pharisees take great delight in criticizing Jesus for associating with “sinners” such as tax collectors, prostitutes, lepers, and Samaritans whom they categorize as unclean, unlike themselves. And we all know what Jesus thought of their attitude. But the whole issue of food became a major stumbling block for the early Jewish Christians, as several incidents in the Book of Acts attest. But God pronounced the definitive word on the subject when he presented Peter with a rooftop vision that in one fell swoop laid to rest both the issue of clean and unclean food and of clean and unclean people groups. (see Acts 10).
All that is not to say that the issue of clean and unclean human beings was a moot point, but it was redefined by Jesus in terms of the ultimate divisions between believers and non-believers at the Last Judgment using images such as the sheep and the goats, the faithful and non-faithful bridesmaids, or the gulf between Lazarus and the rich man. And to make the point even more abundantly clear, read the final chapters of Revelation (21:7-8,27; 22:14-15) describing the greatest divide of all.
Intermarriage
A final type of divine prohibition against mixing is this category. This theme begins with regulations involving animals. A mixed team of an ox and an ass is not to be employed for plowing (Deuteronomy 22:10); experiments in interbreeding animals are not to be carried out (Leviticus 19:19); and humans are not to have sexual intercourse with animals (Exodus 22:19; Leviticus 18:23, 20:15-16).
The whole issue of intermarriage between the people of God and those of neighboring cultures seems not to have been a very big issue in the days of the patriarchs, although it always came with the danger that the purity of religion would be affected. The prime example of that happening later on in Israelite history is King Solomon and his sad end when he was seduced by foreign gods due to his many pagan wives.
But by the time of the return from Exile, this issue became of prime concern for Jewish leaders such as Ezra and Nehemiah (see Ezra 9-10; Nehemiah 9:30;13:23-27), who even went to the extent of enforcing divorce decrees to set aside existing marriages. We would expect that trend to continue into NT times, and we would not be mistaken. The religious leaders of the day were fairly fanatical in seeing that the Jews avoided almost any sort of interactions with non-Jews. And the nearby Samaritans were included in that category.
However, as mentioned above, there is also a strong counter trend in the NT away from all distinctions based on national origins. For one thing, Paul (unlike Ezra and Nehemiah) specifically does not counsel divorce for existing marriage alliances between believers and non-believers (I Corinthians 7:14-15). And finally, Jesus informs the Sadducees that in heaven there will be neither marriage or giving in marriage (Mark 12:25).
Finally, the one apparent counter-counter-trend in the NT back to more restrictions in this matter is found in II Corinthians 22:10, but that is the subject of yet another post.