After confessing “the holy catholic Church,” the Apostles’ Creed adds “the communion of saints.” In a certain sense this article is a further explanation of the preceding: “What is the Church if not the assembly of all the saints?” The communion of saints is the Church.
“Since all the faithful form one body, the good of each is communicated to the others…. We must therefore believe that there exists a communion of goods in the Church. But the most important member is Christ, since he is the head…. Therefore, the riches of Christ are communicated to all the members, through the sacraments.” “As this Church is governed by one and the same Spirit, all the goods she has received necessarily become a common fund.”
The term “communion of saints” therefore has two closely linked meanings: communion in holy things (sancta)” and “among holy persons (sancti).
“Sancta sancti’s! (“God’s holy gifts for God’s holy people”) is proclaimed by the celebrant in most Eastern liturgies during the elevation of the holy Gifts before the distribution of communion. the faithful (sancta) are fed by Christ’s holy body and blood (sancta) to grow in the communion of the Holy Spirit (koinonia) and to communicate it to the world.
In the primitive community of Jerusalem, the disciples “devoted themselves to the apostles’ teaching and fellowship, to the breaking of the bread and the prayers.”
Communion in the faith. the faith of the faithful is the faith of the Church, received from the apostles. Faith is a treasure of life which is enriched by being shared.
Communion of the sacraments. “The fruit of all the sacraments belongs to all the faithful. All the sacraments are sacred links uniting the faithful with one another and binding them to Jesus Christ, and above all Baptism, the gate by which we enter into the Church. the communion of saints must be understood as the communion of the sacraments…. the name ‘communion’ can be applied to all of them, for they unite us to God…. But this name is better suited to the Eucharist than to any other, because it is primarily the Eucharist that brings this communion about.”
Communion of charisms. Within the communion of the Church, the Holy Spirit “distributes special graces among the faithful of every rank” for the building up of the Church. Now, “to each is given the manifestation of the Spirit for the common good.”
“They had everything in common.” “Everything the true Christian has is to be regarded as a good possessed in common with everyone else. All Christians should be ready and eager to come to the help of the needy . . . and of their neighbors in want.” A Christian is a steward of the Lord’s goods.
Communion in charity. In the sanctorum communio, “None of us lives to himself, and none of us dies to himself.”If one member suffers, all suffer together; if one member is honored, all rejoice together. Now you are the body of Christ and individually members of it.” “Charity does not insist on its own way.” In this solidarity with all men, living or dead, which is founded on the communion of saints, the least of our acts done in charity redounds to the profit of all. Every sin harms this communion.
From the Catechism of the Catholic Church 946-953