Catechism of the Catholic Church
a, b, c, and d. Para. 950: ". . . 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" (Roman Catechism I, 10, 24).
Para. 951: 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 (LG 12 § 2). Now, "to each is given the manifestation of the Spirit for the common good" (1 Cor 12:7).
Para. 952: "They had everything in common" (Acts 4:32). "Everything the true Christian has it 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" (Roman Catechism I, 10, 27). A Christian is a steward of the Lord's goods (Cf. Lk 16:1, 3).
Para. 953: Communion in charity. In the sanctorum communio, "None of us lives to himself, and none of us dies to himself" (Rom 14:7). "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" (1 Cor 12:26-27). "Charity does not insist on its own way" (1 Cor 13:5; cf. 10:24). 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.
Para. 956: The intercession of the saints. "Being more closely united to Christ, those who dwell in heaven fix the whole Church more firmly in holiness. . . . [T]hey do not cease to intercede with the Father for us, as they proffer the merits which they acquired on earth through the one mediator between God and men, Christ Jesus. . . . So by their fraternal concern is our weakness greatly helped" (LG 49; cf. 1 Tim 2:5).