A response to a Christian article on the wool-linen prohibition — clarifying its halachic scope, the major rabbinic readings, and the importance of not casually dismissing ancient Jewish law.
Summary. The shaatnez prohibition (Vayikra 19:19, Devarim 22:11) forbids the weaving of wool and linen together. The article works through Rashi's pure-obedience reading, Rambam's rationalist account of shaatnez as marked priestly attire transposed away from pagan use, and the Ramban's mystical hybrid view. The author corrects the framing of "giving lay people access to priestly symbology" — it is rather that all Israel is a nation of priests with varying access to divine symbology — and pushes back on a Christian author's casual dismissal of the law.
The Article (Verbatim)
I ran across your article: What's So Wrong with Mixing Wool & Linen?
It's good reading. A few things I might add, through the lens of Jewish Orthodoxy:
First, a practical note: "wool", here, only applies to sheep wool, and no other variant. And, the wearing of wool over linen is not proscribed. Only the weaving of them together is.
It's true that shaatnez (the wool-linen prohibition) and tzitzit are connected through priestly symbolism. But the shaatnez is also classified as a "chok" mitzvah, a law/righteous-act that was given without explanation. The canonical literature (Tanakh/Bible, Oral Torah/Talmud, Midrash, Commentaries, Halachic literature, Machshava, Kabbalah, Mussar) on the chukim is deep and engaging reading, and varies widely. On the one hand, the medieval French scholar Rashi, says these laws are for the sake of binding ourselves to G-d only, and for no other reason ("obedience" if you will). G-d asked it, and we do it. To question why is a category error.
Opposite Rashi and two centuries later comes Maimonides (Rambam with an "m"). Being a rationalist, he argued that every law had a reason in historical context, and that shaatnez was forbidden to lay people because it was part of a triumvirate (animal wool, plant product, and metal) that pagan Canaanite priests wore. He then argued that it was transposed onto Levite priests for the same reason that animal sacrifice was instituted (and even the mishkan/tabernacle) as a compromise between G-d and the people, to allow them some of the familiar mechanics of pagan practice, but realigned to the worship of Hashem, and (as your article states) strictly scoped to the priestly class as part of the compromise (surely to prevent fractious adventurism of the kind we saw in 19th Century Christianity, where the opinion of any person was as good as anyone else's, and competing sects multiplied).
Then we have Nachmanides (Ramban with an "n") aligning with Rambam that chukim do all have reasons—but that they are mystical and metaphysical.
There are other hybrid views along this spectrum.
This may seem like splitting hairs, but it's an important distinction: "Giving the lay people access to priestly symbology" is an incorrect framing. It is, rather, giving the lay people, and the priests, varying degrees of access to divine symbology.
Your reading of Korach is, by the lights of most all rabbinic commentary, off the mark. One of my favorite modern scholars, Rabbi Lord Jonathan Sacks of blessed memory (former Chief Rabbi to the UK), is representative of the consensus view: Korach was not being genuine, but instead was building a straw man. (A straw-man example unfortunately replicated over and over in the New Testament, ascribed to the Pharisees, in one of several antisemitic tropes that have bathed the New Testament in so much Jewish blood.) Because this mitzvah is a chok, there is no deeper halachic answer for Korach. Why doesn't a purely blue cloak satisfy the blue strand in the tzitzit? Because, simply, G-d did not command us to wear blue cloaks, but he did command us to wear tzitzit.
The framing of Israel being a nation of priests is accurate, foundational, and apparent in the number of mitzvot given to the lay people, and indeed, allusions to divine holiness in symbols like the tzitzit. It emerges even more powerfully in Kabbalah. It is (adding my own commentary) surely a weighty reason the Jews have survived for 3K years while every other people and nation (excepting, with caveats, the Hindus) has died, been subsumed, or transformed beyond recognition.
I will say, gently and respectfully, that I don't think you do yourself or Christianity any favors by rolling your eyes at any ancient Jewish law. Christianity—universally and unequivocally—appropriates its doctrinal foundations and its legitimacy from Judaism. That means that: to interpret the Old Testament without the benefit of at least that oral tradition and literature present around 30 CE is to have only a sliver of the full picture, and thus be ignorant of what Christianity claims its own heritage to truly be; and even believing that Jesus was the Mashiach and that he (in an innovative and un-prophesied move, it should be said) deprecated most of the original law, the claim is still that the original law was given by G-d, and so to roll one's eyes at it is to either roll one's eyes at G-d, or to undermine Christianity's central claim to legitimacy.
But, these are productive discussions, and I thank you for your efforts.
Where Denominations Diverge
Orthodox observance of shaatnez requires laboratory testing of garments (shaatnez laboratories operate worldwide). Conservative practice generally observes the prohibition. Reform Judaism does not require shaatnez observance, though some Reform Jews do observe it as a meaningful chok.
Sources Cited in the Article
Torah: Vayikra 19:19; Devarim 22:11.
Rashi on Vayikra 18:4 (the classical reading of chukim as pure obedience).
Rambam, Moreh Nevuchim III:26, III:37 (chukim with rational reasons).
Ramban (Nachmanides), Commentary on Vayikra 19:19 (chukim as mystical/metaphysical).
Bamidbar 16 (Korach narrative).
Rabbi Lord Jonathan Sacks, Covenant & Conversation: Numbers (on Korach).
Sefer HaChinukh, Mitzvah 551 (shaatnez).
Further Reading
Yeshayahu Leibowitz, Judaism, Human Values, and the Jewish State (on chukim and rationality).
Joseph Soloveitchik, The Halakhic Mind.