צמר ופשתים יחדו לפי שבאה תקלה ע״י שניהם נאסרו להיות בבת אחת הבל הביא מבכורות צאנו קין הביא מזרע פשתן. ד״א לפי שמשניהם בגדי כהונה הזהירם ללבשם בחול רק למשרתיו בשעת עבודתן ולכך לא נמצא נגע רק בבגד צמר ובגד פשתים להראות שיש פשע בכלאים. אהדריה קרא ללמדך דשעטנז היינו צמר ופשתים. צמר ופשתים יחדו, “wool and linen together.” The reason why only these two categories of yarns are forbidden to be mixed is that the two were involved in the first murder. Kayin’s offering to G-d had consisted of leftover flax that he had grown, while Hevel had offered sheep which grow wool. Seeing that these two species had been indirectly responsible for the first disagreement between two human beings ending in the death of one, we are to be forever mindful of this. An alternate interpretation: These two fibers were used in the garments worn by the priests when performing service in the Temple but are not permitted to be worn by the priests at any other times. This is why the affliction known as tzoraat, does not strike garments consisting of any other fibers. This is a reminder that there is a basic problem involving these fibers, one that is overcome only on holy consecrated ground when used by the priests in their service to G-d. The Torah teaches that the expression shatnes, means a mixture of woolen and flax (linen) fibers.