Gemara: "The man was, at the time of Shaul, an elder, who came with people" (Shmuel I:17:12). This is Yishai the father of David, who would go out with an ochlusa (a very large group), would enter with an ochlusa, and would teach with an ochlusa.

Ein Ayah:The great man who is fit to serve as a pillar of his nation is, by his nature, a communal person. Therefore, when he impacts on those who are out of his inner circle, it should influence a very large group, so that he helps the whole nation take the actions that they should. In the realm of thoughts, too, his ideas will be sought by many because he is not able to limit himself to small groups. It is appropriate that one whose offspring would form a dynasty of kings of Israel would be particularly focused on the communal/national and would cast light on the glorious nation as a whole.
The going out of Yishai refers to influence on others, the entering refers to impact on actions, and the teaching refers to the sharing of ideas that connect him to the lot of the nation, its happiness, and spiritual flourishing. This is the "came with people" to which the pasuk refers.
However, there is a condition. Such an influential person should be "an elder who came with people." In other words, it is someone who already acquired much life experience and controls his various emotions. When youngsters, who still need to teach themselves morality, express opinions for the whole nation, this is potentially damaging. That is why "I will make youngsters your officers" (Yeshaya 3:4) is a curse. Only one with experience in addition to wisdom is fit to come among the masses and teach them.


The Requirements for a Holy Convocation
(condensed from Ein Ayah, Berachot 9:289)

Gemara:We have learned: There is no ochlusa [upon which one makes the beracha of "Baruch chacham harazim"] in Bavel. We have learned: There is no ochlusa of less than 600,000 people.

Ein Ayah:In order to have an element of klal (communal) on the highest level, there need to be all the elements that turn a community into a full nation. In the case of Hashem’s nation, a specific Land and number of people are needed to be a great and holy nation.
The Land must be special in its holiness, its historical value, and its physical characteristics for its inhabitants to form an ochlusa. In Bavel, where the Jews are in exile, under foreign rule, they cannot form a nation. Communal affairs do not take on a national characteristic. The grandeur that accompanies nationhood and makes it appropriate to bless on the harmony between complementary elements of the different thoughts of the mass of people is thus missing in Bavel.
Even if there is an assembly in the Land, if there are not enough people to create a national context, it is not an ochlusa, which demonstrates Hashem’s greatness. 600,000 is the number that was needed to create a nation when we came out of Egypt. The requirements for nationhood remain over the generations, as there is always a requirement that Hashem’s Name be called upon us. There must be enough opinions and subgroups for the national identity to exist. With less than that, we lack the unique status to stand up with scorn to all our opponents.
When the number is present in Eretz Yisrael, then the stature of the House of Jacob can grow and we will be fit to receive and carry out the Torah as a nation before Hashem.