The prohibitions of kilayim and sha’atnez are divine statutes whose essential meaning lies beyond human understanding. Even so, the Sages throughout the generations have proposed various explanations for the mitzva. The central explanation is that wool and linen possess different qualities and each has its own purpose; God therefore commanded us to give each its proper place and not mix them (Ramban, Vayikra 19:19).
Wool and linen were the two principal materials used for clothing, yet they differ fundamentally and even stand in opposition. Wool comes from the animal world and alludes to the attribute of ḥesed, while linen comes from the plant world and alludes to the attribute of din; combining them is therefore complex and difficult. The Torah commanded that they be joined only in the context of a mitzva – in the priestly garments and in tzitzit – so that their union takes place in holiness and each power finds its proper expression, adding blessing and life. Moreover, since combining wool and linen is a mitzva in the priestly garments and in tzitzit, it is inappropriate to use this unique union for ordinary purposes, as it is reserved for holiness alone (Da’at Zekenim, Devarim 22:11; Ḥizkuni, Vayikra 19:19; Metzudat David of Radvaz §235; Likutei Halakhot, Kil’ei Begadim 1).
It has also been explained that these opposing forces can find their proper expression only in the context of a mitzva. When they are combined outside that context, their positive potential is constrained and prevented from emerging (Zohar III 86b). Within a mitzva, ḥesed and din are expressed properly; when mixed indiscriminately, however, the evil inclination turns them to harmful ends (Mikhtav Me-Eliyahu IV, p. 176). When a person ought to give tzedaka, for example, the evil inclination may cloak itself in din and argue that the poor person is undeserving. Conversely, when one must stand for truth and rescue someone being exploited by an oppressor, the evil inclination may cloak itself in ḥesed and find merit in the oppressor, thereby evading the obligation to help the victim.
It may be suggested that by separating wool and linen – the two natural fibers best suited for clothing – and permitting their union only in the context of a mitzva, the Torah taught humanity to develop additional fibers in which the human role in combining and shaping natural properties is more pronounced. Combining such fibers is therefore straightforward and carries neither a prohibition nor a mitzva.[12]
