Answer: On one hand there is a desire to receive pleasure, and on the other hand, there is the Light, the Creator. Both have to be connected as one. And in order to bring them to unity, a system was created: family, society, this world, and the upper worlds, the whole Universe, all that exists.
But in face, this process involves only two: the desire to receive and desire to bestow. In order to tie them together and bring unity between them, all the medium through which they should connect were built. There is a person on one side, and there is the Creator on the other. In the middle, there is a family, the society, the group, humanity, history and the whole system of upper worlds and their actions. All that is between them is in order to connect them with each other.
If a person wants to become connected with the Creator, then the only opportunity to test himself is through the group, meaning, through the worlds that exist between him and the Creator. Only by that can they connect.
From the 1st part of the Daily Kabbalah Lesson 8/5/12, Writings of Baal HaSulam