In the Torah portion Shemini,1 we learn about spiritual impurity as it pertains to food. The Rambam2 explains that a number of conditions must be met before food becomes spiritually impure:

Regarding food in general: a) it must be specifically intended for human consumption; b) the food must first have been soaked in liquid.

Furthermore, plants can only become impure after they are uprooted; as long as they are attached, even if by only one thin root, and as long as that root serves to convey nourishment, they are incapable of becoming impure.

All Torah laws serve as lessons in man’s Divine service, for besides the actual laws, there are spiritual lessons to be learned therein as well.3 How are we to understand the above laws in terms of our spiritual service?

The entire concept of spiritual impurity only exists in relation to holiness. Since the forces of unholiness receive only a minimal life-force from above, they constantly seek to increase their vitality. This is done by latching onto an individual who has a greater degree of holiness than they, and making that person sin. The individual’s consequent descent into spiritual impurity and unholiness gives the dark forces an extra measure of life.

It thus follows that only food intended for human consumption can become spiritually impure. That is, only the spiritual aspects of man are subject to impurity. For, in a broader sense, “food” alludes to all of man’s needs,4 and the true life of man is his soul, with its spiritual needs — its food — being Torah study and the performance of mitzvos.

Then comes the second condition: that even this spiritual level is not subject to impurity until it is “soaked in liquid.”

How are we to understand this?

Liquid, with its propensity for flowing from on high,5 denotes beneficence, wherein he that is on a higher plane descends to one who is on a lower level. In spiritual terms, this refers to an individual who does not keep his spirituality to himself (i.e. he is not “arid”), but descends and shares with those on lower levels.

Thus, when “man’s food,” his Torah and mitzvos, display the characteristics of liquid and descend to his fellow so that his neighbor too can become more spiritual, this increases his own measure of holiness. As a result, unholiness tries even harder to secure nourishment from such a person.

But this would mean that the more a person seeks to spiritually benefit not only himself but also his environment, the more exposed he will become to the blandishments of unholiness! This seems patently unfair.

This complaint is removed by the third condition: Plants, as long as they are attached… are incapable of becoming impure. In spiritual terms, this means that, as long as a man’s service remains attached to its source and root in his soul’s essence, he cannot become impure.

All of a Jew’s spiritual actions derive from their “root and source,” the essence of his soul, from whence emanates his Jewishness, his unshakable faith in G‑d and his capacity to serve Him with total self-sacrifice. At this level, it is impossible for a person to become impure.

Man’s “food,” i.e., his spiritual service, must thus be constantly connected to its “root,” the essential aspect of his soul. It is not enough that the “root” remains whole; the faith and self-sacrifice stemming from it must permeate his spiritual activity.

When a Jew lives in this manner, even if all that remains is “one thin root” (i.e., all other roots have — Heaven forbid — been sundered), the person can rest assured that he will derive nourishment from his soul’s essence. For, since this remaining root is attached to the soul’s essence in a manner by which growth can be nurtured, the individual can be confident that he will remain unsullied and pure.

Based on Likkutei Sichos, Vol. XXVII, pp. 74-78