Catechism of the Catholic Church

"The Church, in Christ, is like a sacrament-a sign and instrument, that is, of communion with God and of unity among all men." The Church's first purpose is to be the sacrament of (360) the inner union of men with God. Because men's communion with one another is rooted in that union with God, the Church is also the sacrament of the unity of the human race. In her, this unity is already begun, since she gathers men "from every nation, from all tribes and peoples and tongues"; at the same time, the Church is the "sign and instrument" of the full realization of the unity yet to come.