Answer: The transitional phase between this world and the spiritual world is the physical group where we can begin to establish spiritual laws. This is a wonder in this world: deeds which are Lo Lishma (for my sake) can bring us to Lishma (to bestowal).
In other words, we do all kinds of deeds artificially, with false bestowal. Yet they advance us because there is a transitional level between the spiritual world and this world. This intermediary level is a person who is comprised of two parts: one within the other. Therefore it is possible to build an external group of people to carry out external actions and to awaken internal actions within them. This is as if we have two parts from different worlds in one “medium.”
And therefore a collection of people, a Minyan (ten people), become the ten Sefirot that intervene between this world and the upper world.