Gemara:


Ein Ayah: The joining together of many people has significant value only if it contains an element of ethical improvement. If we will give value to a group just from the material perspective, there is little chance of it helping reach piety or unity, for on a materialistic level, people’s material desires are individualistic. In contrast, ethical goals of wisdom and benevolence link all together and cause individuals to strive for the betterment of the masses. When one sees the impact of spiritual aspirations, even an individual will be filled with a desire to join and feel optimistic about the prospect of communal spiritual advancement.
A congregation requires spiritual guidance to have a lasting effect. There is a difference between those who see material gains as their main aspiration and give a place for spiritual guidance to keep things running smoothly, and between those who see righteousness as the purpose of forming the group. After all, only in the spiritual realm is the power of the congregation most significant. Those who are interested in material success will minimize the place of wisdom, whereas those who are interested in spirituality will strive to increase wisdom and the number of people who promulgate it. They will not be satisfied with the minimum needed to lead in a direction of spirituality but will want to have more of that good thing. With this attitude, the group will have a special power.
This is the reason to have ten, the minimum number for a congregation, including two rabbis. While in the context of leadership, there is an advantage in having exactly one leader for a group, when the matter is giving complete thanks to Hashem, the presence of more rabbis increases the insight that can make these thanks complete.

Leaders from Within the Group
(condensed from Ein Ayah, Berachot 9:19)

Gemara:


Ein Ayah: The love we have for a community is based on a realization that an individual cannot reach his goals alone. Therefore, societies need many rules, whether those imposed by the Torah or those imposed by convention. With a group comprised only of rabbis, one might not realize the broad, basic importance of a congregation of people.
Scholars, upon realizing the spiritual advantages they have, may want to be separate from the rest of the people, so that they can reach greater spiritual heights than those found within regular society. However, the community is not built by such people. Rather true spiritual impact comes from those who are counted as part of the congregation. That is why the number ten includes rabbis within the count of the group.
There are scholars of an unusually high level, who cannot be included among those who are too far beneath them. These people give off so much light that it is proper that they ‘shine on the masses’ even from a distance. The problem is that regular people are too removed from them to discern their impact. Therefore, the one who is trying to use the presence of the rabbis to elevate his thanks of Hashem should use the type of rabbi who is close enough to his level so that they can relate to each other.