"And Moshe spoke to Hashem saying: Let Hashem, the G-d of the spirits of all flesh, set a man over the congregation. And Hashem said to Moshe: Take Yehoshua, a man with spirit in him."
The description "G-d of the spirits of all flesh" and the unique connection between this title and Moshe Rabbenu's request for a leader for the people is explained by the Netziv in Ha'amek Dovor: "A spirit for all flesh means that his spirit is pliant and malleable like meat, which is soft. The spirit can also be likened to flesh in that it is drawn to and driven by its personal pleasure and benefit. A person cannot help but follow what he feels is pleasurable. This is why it is difficult to truly lead the people. They require a person who is strong-minded but not subject to personal interests."
Moshe Rabbenu incorporates within his words the deepest roots from which are derived the need for a suitable leader for the Jewish people. This need for one leader arises from the very fact that people are different and have different opinions. They must have a single authoritative figure to lay down the law. The reason why people vary is because their spirits are like flesh -- soft, changeable, pliable -- and they tend to seek what is personally best for them. If people were able to dissociate and neutralize themselves from personal interests to see the common good, they would readily be able to find a leader to conduct them.
Everything we need to know about what is permissible or not is to be found in the Torah and the leader need only see that the Torah is carried out and applied to life's situations. However, the fact that the spirit's will is dictated to by the flesh, and that the flesh must look through the physical eyes of the body which is purely selfish, causes vision to be distorted so that even Truth is subject to interpretation.
Thus, it is the duty of the leader to decide which is the correct opinion, the proper outlook. He must have clarity of vision and not be swayed by personal interests. He must be strong, levelheaded and not weak in spirit. This is how Moshe Rabbenu diagnosed the ultimate qualities of leadership, and this is what he prayed that he find reposing in one person. And he did.
Hashem indicated Yehoshua as the full personification of the proper character traits. How? "And Hashem said to Moshe: Take Yehoshua bin Nun, a man in whom there is spirit." Says the Netziv: "He has spirit, that is, his disinterested opinion, his mind, stands independent and is not subject to his desires for personal benefit, nor is he moved by outside pressures of the will of others."
Secular leaders are chosen by their past records or, alternately, in accordance with their followers and supporters. A Jewish leader merits the stature of "a man over the congregation" on the basis of a single, comprehensive attribute: honesty. Disinterestedness. Clean hands.
In its biographical comments regarding Yehoshua, the Torah mentions one thing alone: " . . . who has spirit in him." He has a mind of his own; he stands firm, does not bend to the wills of others or even to his own self interest. This trait enables him to see everything through eyes of the spirit and not of the flesh, or even a mingling of both. He can view the bare truth, clean, uncontaminated, in its essential purity.
This concept is further honed by Maran R' Elchonon Wassermann Hy'd, who writes, "We are warned by the Torah that a judge must despise graft. What really does it matter, so long as everyone knows that bribery is forbidden and is certain that he did not accept any gifts in any court case. Does it make a difference whether he loves money in his personal life? Yes, it does, because a person who loves money has his eyes already blinded; he is biased. A weak-willed person is willy-nilly driven by his drives and they affect every step of his life.
"A person encounters decisions involving personal interests all the time and if he cannot think straight, with disinterest, he is necessarily biased and self-prejudiced. His intellect bends to his will and becomes distorted. His vision becomes so crooked that even when it comes to judging something that does not affect him in the least, it is already contaminated and off kilter. So we see that not only is it necessary for a judge or leader to divorce himself from self, from personal interests, but he must also be clean and free of biased interests in every single area of his life. He must be purely and completely objective in order to think and see straight."
These traits are a thread that runs through the biographies of all Jewish leaders throughout the generations, of those individuals who were appointed over the congregation. They never consider themselves; they are divorced of any tendencies involving personal benefits, nor are they swayed by pressure from others who are out for their own good and not for the communal welfare. And, as R' Elchonon stressed, this is expressed by a total purity of interests. They are clean -- in every single aspect of their own lives.