The gathering together of the People of God began at the moment when sin destroyed the communion of men with God, and that of men among themselves. The gathering together of the Church is, as it were, God's reaction to the chaos provoked by sin. This reunification is achieved secretly in the heart of all peoples: "In every nation anyone who fears him and does what is right is acceptable" to God.

In keeping with the social nature of man, the good of each individual is necessarily related to the common good, which in turn can be defined only in reference to the human person.  Do not live entirely isolated, having retreated into yourselves, as if you were already justified, but gather instead to seek the common good together.

By common good is to be understood "the sum total of social conditions which allow people, either as groups or as individuals, to reach their fulfillment more fully and more easily." The common good concerns the life of all. It consists of three essential elements.
First, the common good presupposes respect for the person as such. Second, the common good requires the social well-being and development of the group itself. Finally, the common good requires peace, that is, the stability and security of a just order.

Participation is the voluntary and generous engagement of a person in social interchange. It is necessary that all participate, each according to his position and role, in promoting the common good. This obligation is inherent in the dignity of the human person.

From the Catechism of the Catholic Church
Part 3, Section 1, Chapter 2, Article 2