From the Catechism of the Catholic Church, Simplified
Forming One Body (946-948)
The doctrine of the “Communion of Saints” helps to explain the Church.
The baptised all form one body and the good of each is shared by all. “Because Christ (the Church’s most important member) is the head, his riches are given to all the members through the sacraments” (St Thomas Aquinas).
The Church has all her riches in a “common fund.” Her two-fold communion is both “in holy things” and “among holy persons.” “God’s holy gifts for God’s holy people” (Elevation Proclamation in Eastern liturgies).
Five Communions (949-953)
The disciples “devoted themselves to the apostles’ teaching and fellowship, to the breaking of the bread, and the prayers” (Acts 2:42).
There are five Communions:
Communion in the faith – This faith of the Church was received from the apostles.
Communion of the sacraments – Sacraments, especially Baptism, link all the faithful to each other and to Christ. The word “communion” “is especially “suited for the Eucharist which brings about this communion” (Roman Catechism).
Communion of charisms – These are “manifestations given by the Spirit for the common good” (1 Cor 12:7).
Communion of common goods – Whatever a Christian has is really possessed in common with everyone else.
Communion in charity – “If one members suffers, all suffer together; if one member is honored, all rejoice together” (1 Cor 12:26).
Three States of the Church (954-956)
Right now there are three states of the Church. Some disciples are on earth, others have died and are being purified, and others are in full glory.
A union exists between believers who are still on this earth and those who have died. This union is reinforced by an exchange of spiritual goods. “Yet, we all form one Church and in Christ we cleave together” (Second Vatican Council).
Saints in Heaven (957-958)
The saints in heaven establish the whole Church in holiness. Their merits are offered through Christ, the one Mediator. By their concern, our weaknesses are helped. “Do not weep, for I shall be more useful to you after my death” (St. Dominic). “I want to spend my heaven in doing good on earth” (St. Therese of Lisieux).
Our union with the saints in heaven joins us to Christ. “We love the martyrs. May we also be their companions and fellow disciples” (Martyrdom of Polycarp).
Souls in Purgatory (959)
The Church has always had great respect for the dead. “It is a holy and wholesome thought to pray for the dead that they may be loosed from their sins” (2 Macc 12:45). By our prayers, we help them and make their intercession for us effective.
Because she joins with Christ in bringing about the birth of believers, Mary is both Mother of Christ and Mother of the Church.
The lives of the Saints are indexed by month.