35 Christ, the great Prophet, who proclaimed the Kingdom of His Father both by the testimony of His life and the power of His words, continually fulfills His prophetic office until the complete manifestation of glory. He does this not only through the hierarchy who teach in His name and with His authority, but also through the laity whom He made His witnesses and to whom He gave understanding of the faith (sensu fidei) and an attractiveness in speech so that the power of the Gospel might shine forth in their daily social and family life. They conduct themselves as children of the promise, and thus strong in faith and in hope they make the most of the present, and with patience await the glory that is to come. Let them not, then, hide this hope in the depths of their hearts, but even in the program of their secular life let them express it by a continual conversion and by wrestling "against the world-rulers of this darkness, against the spiritual forces of wickedness. Just as the sacraments of the New Law, by which the life and the apostolate of the faithful are nourished, prefigure a new heaven and a new earth, so too the laity go forth as powerful proclaimers of a faith in things to be hoped for, when they courageously join to their profession of faith a life springing from faith. This evangelization, that is, this announcing of Christ by a living testimony as well as by the spoken word, takes on a specific quality and a special force in that it is carried out in the ordinary surroundings of the world. In connection with the prophetic function is that state of life which is sanctified by a special sacrament obviously of great importance, namely, married and family life. For where Christianity pervades the entire mode of family life, and gradually transforms it, one will find there both the practice and an excellent school of the lay apostolate. In such a home husbands and wives find their proper vocation in being witnesses of the faith and love of Christ to one another and to their children. The Christian family loudly proclaims both the present virtues of the Kingdom of God and the hope of a blessed life to come. Thus by its example and its witness it accuses the world of sin and enlightens those who seek the truth. Consequently, even when preoccupied with temporal cares, the laity can and must perform a work of great value for the evangelization of the world. For even if some of them have to fulfill their religious duties on their own, when there are no sacred ministers or in times of persecution; and even if many of them devote all their energies to apostolic work; still it remains for each one of them to cooperate in the external spread and the dynamic growth of the Kingdom of Christ in the world. Therefore, let the laity devotedly strive to acquire a more profound grasp of revealed truth, and let them insistently beg of God the gift of wisdom.
Source: Lumen Gentium (Vatican.va)