From Pope St. John Paul II’s Apostolic Exhortation Familiaris Consortio (1981):
The Church, a prophetic, priestly and kingly people, is endowed with the mission of bringing all human beings to accept the word of God in faith, to celebrate and profess it in the sacraments and in prayer, and to give expression to it in the concrete realities of life in accordance with the gift and new commandment of love.
The law of Christian life is to be found not in a written code, but in the personal action of the Holy Spirit who inspires and guides the Christian. It is the “law of the Spirit of life in Christ Jesus”;159 “God’s love has been poured into our hearts through the Holy Spirit who has been given to us.”160
This is true also for the Christian couple and family. Their guide and rule of life is the Spirit of Jesus poured into their hearts in the celebration of the sacrament of Matrimony. In continuity with Baptism in water and the Spirit, marriage sets forth anew the evangelical law of love, and with the gift of the Spirit engraves it more profoundly on the hearts of Christian husbands and wives. Their love, purified and saved, is a fruit of the Spirit acting in the hearts of believers and constituting, at the same time, the fundamental commandment of their moral life to be lived in responsible freedom.
Thus, the Christian family is inspired and guide by the new law of the Spirit and, in intimate communion with the Church, the kingly people, it is called to exercise its “service” of love towards God and towards its fellow human beings. Just as Christ exercises His royal power by serving us,161 so also the Christian finds the authentic meaning of his participation in the kingship of his Lord in sharing His spirit and practice of service to man. “Christ has communicated this power to his disciples that they might be established in royal freedom and that by self-denial and a holy life they might conquer the reign of sin in themselves (cf. Rom. 6:12). Further, He has shared this power so that by serving Him in their fellow human beings they might through humility and patience lead their brothers and sisters to that King whom to serve is to reign. For the Lord wishes to spread His kingdom by means of the laity also, a kingdom of truth and life, a kingdom of holiness and grace, a kingdom of justice, love and peace. In this kingdom, creation itself will be delivered out of its slavery to corruption and into the freedom of the glory of the children of God (cf. Rom. 8:21).”162
159 Rom 8:2.
160 Rom 5:5.
161 Cf. Mk 10:45.
162 Lumen gentium, 36.
— Familiaris Consortio 63