At the conclusion of the Torah portion of Devarim , Moshe relates how he told the tribes of Reuven and Gad that their warriors were to “go forth ahead of their Jewish brethren”1 and lead them in battle. Rashi explains:2 “Since they were mighty, they would go forth ahead of the Jewish people in battle and the enemies would succumb to them, as is written:3 ‘he tears as prey the arm and head.’ ”

The tribes of Reuven and Gad went “ahead” of the Jewish people in two ways: a) they forged ahead of the other Jews as a separate and distinct entity; b) they also placed themselves at the head of the Jewish army.

In terms of man’s spiritual service, these two methods of doing battle represent two ways of vanquishing the enemy — the evil inclination:4

By “going forth ahead of their Jewish brethren” the warriors of Reuven and Gad placed themselves at much greater risk than the rest of the nation — evidence of mesirus nefesh , total self-sacrifice. In spiritual terms, this translates into divine service that transcends intellect — a manner of service that emanates from the soul’s core.

The other tribes, however, did not place themselves at particular risk. In spiritual terms this relates to a lesser degree of divine service — service limited to one’s comprehension, and which reflects the soul’s more extrinsic levels.

This explains why the children of Gad would “tear as prey the arm and head,” i.e., with one blow they would sever the enemy’s arm and head. When logic is one’s only weapon in the battle against evil, it is impossible to nullify all the forces of darkness with one blow, for a particular manner of service is required in order to defeat each evil power.

But when one calls upon the all-encompassing spiritual power of self-sacrifice, a power so great that it obliterates every aspect of evil, then it is possible to vanquish all the evil — the “arm and head” — at one blow.

Ultimately, even mesirus nefesh alone does not suffice; it is necessary for mesirus nefesh (i.e. the tribes of Gad and Reuven) to influence the intellect, emotion, speech and action (i.e. the other tribes) as well. This is accomplished in two ways:

a) Mesirus nefesh clothes itself in intellect, emotion, etc., so that one’s performance of Torah and mitzvos is fueled by it.5 The main aspect of an individual’s spiritual service remains the day-to-day study of Torah and performance of mitzvos ; mesirus nefesh is invoked merely as a means to enhance this service, and not as an end in itself.6

b) Mesirus nefesh becomes an end unto itself: be it in a situation that requires actual self-sacrifice, or one that requires mesirus nefesh in potentia , such as during the Ne’ilah prayer of Yom Kippur.

This aspect of mesirus nefesh too, although not clothed in intellect and emotion, has the ability to affect them. For, as explained in Tanya,7 when the power of mesirus nefesh is aroused, it automatically affects one’s intellect, emotions, speech and action.

These, then, are the two manners in which the tribes of Gad and Reuven went to war: At the outset of spiritual service they placed themselves at the head of the Jewish army, i.e., mesirus nefesh merely served as the “head” and conductor of the intellect and emotions, etc.

Thereafter came the higher degree of mesirus nefesh , wherein these two tribes would forge ahead on their own. That is, mesirus nefesh was aroused as an entity unto itself.

Based on Likkutei Sichos Vol. IX, pp. 1-13.