CCC 1816: The disciple of Christ must not only keep the faith and live on it, but also profess it, confidently bear witness to it, and spread it: “All however must be prepared to confess Christ before men and to follow him along the way of the Cross, amidst the persecutions which the Church never lacks.” Service of and witness to the faith are necessary for salvation: “So every one who acknowledges me before men, I also will acknowledge before my Father who is in heaven; but whoever denies me before men, I also will deny before my Father who is in heaven.”(Matthew 10:32)
CCC 872: In virtue of their rebirth in Christ there exists among all the Christian faithful a true equality with regard to dignity and the activity whereby all cooperate in the building up of the Body of Christ in accord with each one’s own condition and function.
CCC 900: Since, like all the faithful, lay Christians are entrusted by God with the apostolate by virtue of their Baptism and Confirmation, they have the right and duty, individually or grouped in associations, to work so that the divine message of salvation may be known and accepted by all men throughout the earth. This duty is the more pressing when it is only through them that men can hear the Gospel and know Christ. Their activity in ecclesial communities is so necessary that, for the most part, the apostolate of the pastors cannot be fully effective without it.
CCC 904: Christ . . . fulfills this prophetic office, not only by the hierarchy . . . but also by the laity. He accordingly both establishes them as witnesses and provides them with the sense of the faith [sensus fidei] and the grace of the word” To teach in order to lead others to faith is the task of every preacher and of each believer.
The laity derive the right and duty to the apostolate from their union with Christ the head; incorporated into Christ’s Mystical Body through Baptism and strengthened by the power of the Holy Spirit through Confirmation, they are assigned to the apostolate by the Lord Himself. They are consecrated for the royal priesthood and the holy people (cf. 1 Peter 2:4-10) not only that they may offer spiritual sacrifices in everything they do but also that they may witness to Christ throughout the world. The sacraments, however, especially the most Holy Eucharist, communicate and nourish that charity which is the soul of the entire apostolate.
One engages in the apostolate through the faith, hope, and charity which the Holy Spirit diffuses in the hearts of all members of the Church. Indeed, by the precept of charity, which is the Lord’s greatest commandment, all the faithful are impelled to promote the glory of God through the coming of His kingdom and to obtain eternal life for all men-that they may know the only true God and Him whom He sent, Jesus Christ (cf. John 17:3). On all Christians therefore is laid the preeminent responsibility of working to make the divine message of salvation known and accepted by all men throughout the world.
For the exercise of this apostolate, the Holy Spirit Who sanctifies the people of God through ministry and the sacraments gives the faithful special gifts also (cf. 1 Cor. 12:7), “allotting them to everyone according as He wills” (1 Cor. 12:11) in order that individuals, administering grace to others just as they have received it, may also be “good stewards of the manifold grace of God” (1 Peter 4:10), to build up the whole body in charity (cf. Eph. 4:16). From the acceptance of these charisms, including those which are more elementary, there arise for each believer the right and duty to use them in the Church and in the world for the good of men and the building up of the Church, in the freedom of the Holy Spirit who “breathes where He wills” (John 3:8). This should be done by the laity in communion with their brothers in Christ, especially with their pastors who must make a judgment about the true nature and proper use of these gifts not to extinguish the Spirit but to test all things and hold for what is good (cf. 1 Thess. 5:12,19,21).
The Church was founded for the purpose of spreading the kingdom of Christ throughout the earth for the glory of God the Father, to enable all men to share in His saving redemption,(1) and that through them the whole world might enter into a relationship with Christ. All activity of the Mystical Body directed to the attainment of this goal is called the apostolate, which the Church carries on in various ways through all her members. For the Christian vocation by its very nature is also a vocation to the apostolate. No part of the structure of a living body is merely passive but has a share in the functions as well as life of the body: so, too, in the body of Christ, which is the Church, “the whole body . . . in keeping with the proper activity of each part, derives its increase from its own internal development” (Eph. 4:16).
Indeed, the organic union in this body and the structure of the members are so compact that the member who fails to make his proper contribution to the development of the Church must be said to be useful neither to the Church nor to himself.
In the Church there is a diversity of ministry but a oneness of mission. Christ conferred on the Apostles and their successors the duty of teaching, sanctifying, and ruling in His name and power. But the laity likewise share in the priestly, prophetic, and royal office of Christ and therefore have their own share in the mission of the whole people of God in the Church and in the world.
They exercise the apostolate in fact by their activity directed to the evangelization and sanctification of men and to the penetrating and perfecting of the temporal order through the spirit of the Gospel. In this way, their temporal activity openly bears witness to Christ and promotes the salvation of men. Since the laity, in accordance with their state of life, live in the midst of the world and its concerns, they are called by God to exercise their apostolate in the world like leaven, with the ardor of the spirit of Christ. (Decree on the Apostate of Laity 1:2).
…they should not limit their cooperation to the parochial or diocesan boundaries but strive to extend it to interparochial, interdiocesan, national, and international fields. This is constantly becoming all the more necessary because the daily increase in mobility of populations, reciprocal relationships, and means of communication no longer allow any sector of society to remain closed in upon itself. Thus they should be concerned about the needs of the people of God dispersed throughout the world. They should especially make missionary activity their own by giving material or even personal assistance. It is a duty and honor for Christians to return to God a part of the good things that they receive from Him. (Decree on the Apostolate of Laity 3:10).
For in the Church there are many Apostolic Undertakings which are established by the free choice of the laity and regulated by their prudent judgment. The mission of the Church can be better accomplished in certain circumstances by undertakings of this kind, and therefore they are frequently praised or recommended by the hierarchy. No project, however, may claim the name “Catholic” unless it has obtained the consent of the lawful Church authority. (Decree on the Apostate of Laity 5:24).
Bishops, Pastors of Parishes, and Other Priests of both branches of the clergy should keep in mind that the right and duty to exercise this apostolate is common to all the faithful, both clergy and laity, and that the laity also have their own roles in building up the Church. For this reason they should work fraternally with the laity in and for the Church and take special care of the lay persons in these apostolic works. (Decree on the Apostate of Laity 5:25).
Deserving of special honor and commendation in the Church are those lay people, single or married, who devote themselves with professional experience, either permanently or temporarily, to the service of associations and their activities. There is a source of great joy for the Church in the fact that there is a daily increase in the number of lay persons who offer their personal service to apostolic associations and activities, either within the limits of their own nation or in the international field or especially in Catholic mission communities and in regions where the Church has only recently been implanted. The pastors of the Church should gladly and gratefully welcome these lay persons and make sure that the demands of justice, equity, and charity relative to their status be satisfied to the fullest extent, particularly as regards proper support for them and their families. They should also take care to provide for these lay people the necessary formation, spiritual consolation, and incentive. (Decree on the Apostolate of Laity 4:22).
The most holy council, then, earnestly entreats all the laity in the Lord to answer gladly, nobly, and promptly the more urgent invitation of Christ in this hour and the impulse of the Holy Spirit. Younger persons should feel that this call has been directed to them especially and they should respond to it eagerly and generously. Through this holy synod, the Lord renews His invitation to all the laity to come closer to Him every day, recognizing that what is, is also their own (Phil. 2:5), to associate themselves with Him in His saving mission. Once again, He sends them into every town and place where He will come (cf. Luke 10:1) so that they may show that they are co-workers in the various forms and modes of the one apostolate of the Church, which must be constantly adapted to the new needs of our times. Ever productive as they should be in the work of the Lord, they know that their labor in Him is not in vain (cf. 1 Cor. 15:58).