Many years ago a teacher challenged me to name a mitzvah that had no personal significance. It took but a second for the word shatnez to cross my lips—I just couldn’t think of any spiritual insight that could come from worrying about the fabric blend in my clothes. As a city dweller, I didn’t have much opportunity to practice kilayim by avoiding blending species of seeds in my non-existent garden or breeding different kinds of animals in my imaginary barn. My teacher’s eyes twinkled as he told me that my personal challenge was to find meaning in this mitzvah.

It has taken a few decades, but I think I may have gotten there. For the past year I have been working on a new responsum for the Committee on Jewish Law and Standards called, “Halakhic Perspectives on Genetically Modified Organisms.” Because one of the major forms of genetic engineering involves combining DNA from two or more organisms, the most relevant halakhic category is kilayim, the mixing of breeds, which the Torah forbids this week in Parashat Kedoshim, 19:19.

But even if kilayim turns out to be a useful model for considering the halakhah of genetic engineering, the question remains what spiritual significance can be found in the Torah’s insistence upon species separation. The perspective of this section of the Torah, and of other sections associated with the priestly traditions, is of a tightly ordered world. Time, space, animal species and also human groups are all organized into hierarchical structures. The Torah tells its readers to “guard my statutes by which you shall live.” Part of this regime involves maintaining distinctions in nature and in society.

The most famous half-verse of this portion, and perhaps the most famous phrase in the Torah, comes at 19:18: ”Love your neighbor as yourself; I am the Lord.” But the first half of that verse is equally important: “You shall not take vengeance or bear a grudge against your countrymen.” Leviticus sets a high bar for social solidarity. Even personal experiences of strife must not undermine the bond between Israelites. The next verse begins with a headline: “You shall observe my laws” and what follows is a terse description of the laws of kilayim. Do not breed different species of animals together, do not sow different species of seed together, and do not even wear different kinds of fabrics together. Read as a unit, Leviticus 19:18 and 19:19 imply that maintaining distinctions between kinds of plants, animals and people is essential to social order. Yet this world view of distinctions and hierarchies is severely challenged today.

A prominent feature of our contemporary culture is the eliding of distinctions that have been around for eons. Race, ethnicity, gender and sexual identity, nationality and especially religion are some of the boundaries that have grown more fluid in recent years. Some of the old distinctions were unhealthy and even pernicious. For example, racial bias remains a blight on America society. We all ought to work to achieve what President Lincoln called a more perfect union. The creation of a truly egalitarian society is one of our dearest goals, and the enormous chasm between our ideals and reality inspires us to use our assets of mind, money and social networks to work for social justice.

Yet the Torah’s distinctions, including those of its priestly hierarchy, are not incompatible with a social justice mission. Israel Knoll has observed that the section known to Bible scholars as the holiness source extends the holiness of the priesthood to ordinary Israelites. The priests in the tabernacle are examplars of purity and devotion, but Leviticus shows that even a simple field can become a sanctuary if its bounty is shared with the poor. In other words, distinctions are not so much an engine of exclusion as one of inclusion. By establishing a place in the world and recognizing its inequalities, a person may act more decisively on behalf of others. One key to understanding this is in the curious application of the mitzvah of kilayim.

The priests wear sacred garments, and the high priest is glorious in his attire. But regular Israelites may also, by wearing their tzitzit, become like priests. These garments have the curious feature of being made from blends of white linen and dyed wool (see sources below from M. Eduyot, B. Shabbat and B.Yevamot). In other words, the ordinary mandate to separate linen and wool is set aside for the most exalted garments of Israel. The tzitzit allow a regular person to dress like a priest, just as the farmer’s field can become a sacred space with crops dedicated to the Temple and devoted to the poor. Distinctions between the sacred and profane are made but then unmade at key places so that sanctity can seep into ordinary experience.

In my responsum I show that there seems to be a proliferation of hybrids at the periphery between the sacred and secular zones. In Exodus we read that the cherubim are hybrid creatures that guard the sanctuary, and in Ezekiel and Psalms we learn that they guard the divine throne. Likewise these hybrid creatures block the entrance to the garden of Eden. The cherubim, like the tzitzit, exemplify a kind of blending that is ordinarily forbidden as kilayim.

The Midrash to Shir HaShirim applies the verse, “behold you are lovely” (הנך יפה) to the people Israel when they perform mitzvot. The list includes both ritual and social mitzvot, such as wearing tefillin and sharing food with the poor. It includes the mitzvah of kilayim, and also its evasion with a linen garment and woolen tzitzit. Israel is beautiful in action, and also in contemplation—studying Torah and returning to God. It is beautiful in this world and beautiful in the world to come.

As we read the portions of Aharei Mot and Kedoshim this Shabbat, let’s allow ourselves to slip into a different consciousness where distinctions are honored and occasionally undermined so that the people can truly love others as themselves, and God’s presence can become manifest in our ordinary lives. Then we to may become beautiful in this world, and experience a transformation that is beautiful in the world that is yet to come.

ויקרא פרק יט, יח–יט (יח) לֹא־תִקֹּם וְלֹא־תִטֹּר אֶת־בְּנֵי עַמֶּךָ וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ אֲנִי יְקֹוָק: (יט) אֶת־חֻקֹּתַי תִּשְׁמֹרוּ בְּהֶמְתְּךָ לֹא־תַרְבִּיעַ כִּלְאַיִם שָׂדְךָ לֹא־תִזְרַע כִּלְאָיִם וּבֶגֶד כִּלְאַיִם שַׁעַטְנֵז לֹא יַעֲלֶה עָלֶיךָ:

משנה מסכת עדויות פרק ד משנה י סדין בציצית בית שמאי פוטרין ובית הלל מחייבים:

פירוש המשנה לרמב“ם מסכת עדויות פרק ד משנה י וסדין, בגד פשתן שמתעטפים בו הגברים. בית שמאי אין מחייבין אותו בציצית לפי שהציצית בפשתן שעטנז מחמת התכלת שאינה אלא מן הצמר התכול, וזה מותר ביום שהוא זמן ציצית לפי שאין חובת הציצית אלא ביום שנ‘ וראיתם אותו, ובא בקבלה פרט לכסות לילה. ודרך בני אדם ללבוש טליתותיהם בלילה, ואם לבשו בלילה ויש בו התכלת חייב מלקות לפי שאין אנו אומרים אתי עשה דחי לא תעשה אלא ביום שלבישתו מצות עשה. ובית הלל לא גזרי משום כסות לילה.

תלמוד בבלי מסכת שבת דף קלב עמוד ב אמר רב אשי: היכא אמרינן דאתי עשה ודחי לא תעשה – כגון מילה בצרעת, אי נמי ציצית וכלאים, דבעידנא דמתעקר לאו – קא מוקים עשה. הכא, בעידנא דמתעקר ללאו – לא קא מוקים עשה.

תלמוד בבלי מסכת יבמות דף ד עמוד ב ואמר רחמנא: עביד ליה תכלת, ותכלת עמרא הוא!

ויקרא רבה (וילנא) פרשת אחרי מות פרשה כב לבישת כלאים התרתי לך סדין בציצית

שיר השירים רבה (וילנא) פרשה א א [ט“ו] הנך יפה רעיתי הנך יפה, הנך יפה במצות, הנך יפה בגמילות חסדים, הנך יפה במצות עשה, הנך יפה במצות לא תעשה, הנך יפה במצות הבית בחלוק תרומה ומעשרות, הנך יפה במצות השדה בלקט שכחה ופאה ומעשר עני וההפקר, הנך יפה בכלאים, הנך יפה בסדין בציצית, הנך יפה בנטיעה, הנך יפה בערלה, הנך יפה בנטע רבעי, הנך יפה במילה, הנך יפה בפריעה, הנך יפה בתפלה, הנך יפה בקריאת שמע, הנך יפה במזוזה, הנך יפה בתפילין, הנך יפה בסוכה, הנך יפה בלולב ואתרוג, הנך יפה בתשובה, הנך יפה במעשים טובים, הנך יפה בעולם הזה, הנך יפה בעולם הבא.