ויקרא, פרק י״א, פסוק ל״ז

The laws of purity and impurity draw a sharp distinction between different physical states of food and their connection to the natural world. A fundamental rule is that food cannot become impure unless it has been prepared for human use through contact with water, and as long as it remains an inseparable part of the earth. Seeds and legumes intended for planting remain completely pure simply because they have not yet come into contact with water [רש"י, רשב"ם, אבן עזרא, ביאור יש"ר]. The primary approach among commentators is that dry seeds or fruits are entirely immune to impurity. There is a physical and symbolic logic behind this concept: impurity and dirt easily cling to damp surfaces, but they do not attach to things that are completely dry [רמב"ן, הטור הארוך].

Although the requirement for water is a known principle in these laws, it is emphasized to highlight the absolute nature of this rule. Even direct contact with a severe source of impurity, such as the carcass of a creeping creature, cannot defile a dry seed that lacks the preparation of water [מזרחי, משכיל לדוד, גור אריה]. Furthermore, human intention alone is not enough to change the seed's status. Even if a person plants the seed, showing a clear purpose and valuing the item, this action does not make the seed capable of contracting impurity unless it is first moistened [דברי דוד, תורה תמימה].

A deeper layer of these laws focuses on the seed's connection to the ground. Any plant or seed attached to the earth is entirely shielded from impurity. More remarkably, if a detached seed somehow became impure, planting it initiates a process of total restoration. The moment the seed takes root in the soil, it reconnects to its natural source and is completely cleansed of its impurity, much like the purifying effect of immersion in a ritual bath [רשב"ם, שד"ל, חזקוני, רש"ר הירש, ר' ד"צ הופמן, צפנת פענח, העמק דבר]. This total return to purity takes effect exactly at the moment the seed strikes roots in the earth [מלבי"ם, אדרת אליהו].

These laws also address the physical composition of the seed as it is planted. Seeds are naturally sown along with their protective shells or peels. Because these outer layers guard the inner fruit, they are treated as an integral part of the seed itself. Therefore, the volume of the shell combines with the fruit to meet the minimum size required for food to become susceptible to impurity [תורה תמימה, רלב"ג, רש"ר הירש, אדרת אליהו].

Finally, the physical state of the dead creature transmitting the impurity is just as important. Impurity only transfers to the seed if the piece of the carcass is moist, or if it is dry but capable of being rehydrated when soaked. A completely dry piece that cannot return to a moist state will not transmit impurity [מלבי"ם, אדרת אליהו, פרדס יוסף]. Similarly, dangling limbs that are still attached to an animal do not function as a fallen carcass and therefore do not pass on impurity [תורה תמימה].