4 Since Christ, sent by the Father, is the source and origin of the whole apostolate of the Church, the success of the lay apostolate depends upon the laity's living union with Christ, in keeping with the Lord's words, "He who abides in me, and I in him, bears much fruit, for without me you can do nothing" (John 15:5). This life of intimate union with Christ in the Church is nourished by spiritual aids which are common to all the faithful, especially active participation in the sacred liturgy. These are to be used by the laity in such a way that while correctly fulfilling their secular duties in the ordinary conditions of life, they do not separate union with Christ from their life but rather performing their work according to God's will they grow in that union. In this way the laity must make progress in holiness in a happy and ready spirit, trying prudently and patiently to overcome difficulties. Neither family concerns nor other secular affairs should be irrelevant to their spiritual life, in keeping with the words of the Apostle, "What-ever you do in word or work, do all in the name of the Lord Jesus Christ, giving thanks to God the Father through Him" (Col. 3:17). Such a life requires a continual exercise of faith, hope, and charity. Only by the light of faith and by meditation on the word of God can one always and everywhere recognize God in Whom "we live, and move, and have our being" ( Acts 17:28), seek His will in every event, see Christ in everyone whether he be a relative or a stranger, and make correct judgments about the true meaning and value of temporal things both in themselves and in their relation to man's final goal. They who have this faith live in the hope of the revelation of the sons of God and keep in mind the cross and resurrection of the Lord. In the pilgrimage of this life, hidden with Christ in God and free from enslavement to wealth, they aspire to those riches which remain forever and generously dedicate themselves wholly to the advancement of the kingdom of God and to the reform and improvement of the temporal order in a Christian spirit. Among the trials of this life they find strength in hope, convinced that "the sufferings of the present time are not worthy to be compared with the glory to come that will be revealed in us" (Rom. 8:18). Impelled by divine charity, they do good to all men, especially to those of the household of the faith (cf. Gal. 6:10), laying aside "all malice and all deceit and pretense, and envy, and all slander" (1 Peter 2:1), and thereby they draw men to Christ. This charity of God, "which is poured forth in our hearts by the Holy Spirit who has been given to us" (Rom. 5:5), enables the laity really to express the spirit of the beatitudes in their lives. Following Jesus in His poverty, they are neither depressed by the lack of temporal goods nor inflated by their abundance; imitating Christ in His humility, they have no obsession for empty honors (cf. Gal. 5:26) but seek to please God rather than men, ever ready to leave all things for Christ's sake (cf. Luke 14:26) and to suffer persecution for justice sake (cf. Matt. 5:10), as they remember the words of the Lord, "If anyone wishes to come after me, let him deny himself and take up his cross and follow me" (Matt. 16:24) . Promoting Christian friendship among themselves, they help one another in every need whatsoever. This plan for the spiritual life of the laity should take its particular character from their married or family state or their single or widowed state, from their state of health, and from their professional and social activity. They should not cease to develop earnestly the qualities and talents bestowed on them in accord with these conditions of life, and they should make use of the gifts which they have received from the Holy Spirit. Furthermore, the laity who have followed their vocation and have become members of one of the associations or institutes approved by the Church try faithfully to adopt the special characteristics of the spiritual life which are proper to them as well. They should also hold in high esteem professional skill, family and civic spirit, and the virtues relating to social customs, namely, honesty, justice, sincerity, kindness, and courage, without which no true Christian life can exist. The perfect example of this type of spiritual and apostolic life is the most Blessed Virgin Mary, Queen of Apostles, who while leading the life common to all here on earth, one filled with family concerns and labors, was always intimately united with her Son and in an entirely unique way cooperated in the work of the Savior. Having now been assumed into heaven, with her maternal charity she cares for these brothers of her Son who are still on their earthly pilgrimage and remain involved in dangers and difficulties until they are led into the happy fatherland. All should devoutly venerate her and commend their life and apostolate to her maternal care.
Source: Apostolicam Actuositatem (Vatican.va)