Timothy and Titus, successors of the apostles
The whole Church is apostolic, in that she remains, through the successors of St. Peter and the other apostles, in communion of faith and life with her origin: and in that she is "sent out" into the whole world. All members of the Church share in this mission, though in various ways. "The Christian vocation is, of its nature, a vocation to the apostolate as well." Indeed, we call an apostolate "every activity of the Mystical Body" that aims "to spread the Kingdom of Christ over all the earth." (Vatican II: AA – Apostolicam actuositatem, The apostolate of the laity– 2).
"Christ, sent by the Father, is the source of the Church's whole apostolate"; thus the fruitfulness of apostolate for ordained ministers as well as for lay people clearly depends on their vital union with Christ. In keeping with their vocations, the demands of the times and the various gifts of the Holy Spirit, the apostolate assumes the most varied forms. But charity, drawn from the Eucharist above all, is always "as it were, the soul of the whole apostolate." (AA 3)
The Church is ultimately one, holy, catholic, and apostolic in her deepest and ultimate identity, because it is in her that "the Kingdom of heaven," the "Reign of God," already exists and will be fulfilled at the end of time. The kingdom has come in the person of Christ and grows mysteriously in the hearts of those incorporated into him, until its full eschatological manifestation. Then all those he has redeemed and made "holy and blameless before him in love," (Eph 1:4) will be gathered together as the one People of God, the "Bride of the Lamb," "the holy city Jerusalem coming down out of heaven from God, having the glory of God." For "the wall of the city had twelve foundations, and on them the twelve names of the twelve apostles of the Lamb." (Rv 21:9-11.14).
Saint Louis de Montfort