In the Sequence of the Hexagrams: 'Litigation inevitably causes the multitude to arise; hence it is received with The Army.' The raising of an army arises from dispute, which is why it follows Hexagram 6 (Conflict). As a hexagram, Kun is above and Kan is below.
Spoken in terms of the two trigrams, water in the midst of the earth is the image of the multitude gathering together.
Spoken in terms of the meanings of the two trigrams, danger within and compliance without—treading a perilous path yet moving with compliance—is the meaning of the army.
Spoken in terms of the lines, a single yang line serves as the master of the multitude of yin lines, which is the image of commanding the multitude.
Hexagram 8 (Holding Together) has a single yang line as master of the yin lines above, which is the image of a ruler; The Army has a single yang line as master of the yin lines below, which is the image of a general. The way of the army takes correctness as its foundation.
If one raises an army and mobilizes the multitude to inflict toil upon the world without correctness, the people will not follow; they would only be forcibly driven. Therefore, the army takes steadfastness (zhen) as primary.
Even if its movement is upright, the one commanding it must be an elder; then there is good fortune and freedom from blame.
For there are cases where there is good fortune yet blame, and cases where there is no blame yet no good fortune; only when there is both good fortune and no blame is it consummate goodness. 'The elder' is a title of dignified reverence.
In commanding an army and gathering the multitude, if one is not revered, trusted, and held in awe by the multitude, how can one win the compliance of their hearts?
Thus Sima Rangju, raised from humble obscurity and entrusted with the host, requested Zhuang Jia as overseer because the hearts of the troops were not yet submitted.
What is meant by 'elder' does not necessarily require having always held high rank and noble status; rather, if one's talent, strategy, virtue, and deeds command awe and submission from the multitude, that is an elder.
Once Rangju executed Zhuang Jia, the multitude submitted in awe, and he became an elder. Likewise, the Marquis of Huaiyin rose from humble obscurity to become commander-in-chief, because his strategic wisdom had that which compelled people to revere and fear him.