Lumen Gentium §50

⁵⁰ Fully conscious of this communion of the whole Mystical Body of Jesus Christ, the pilgrim Church from the very first ages of the Christian religion has cultivated with great piety the memory of the dead, and "because it is a holy and wholesome thought to pray for the dead that they may be loosed from their sins", also offers suffrages for them. The Church has always believed that the apostles and Christ's martyrs who had given the supreme witness of faith and charity by the shedding of their blood, are closely joined with us in Christ, and she has always venerated them with special devotion, together with the Blessed Virgin Mary and the holy angels. The Church has piously implored the aid of their intercession. To these were soon added also those who had more closely imitated Christ's virginity and poverty, and finally others whom the outstanding practice of the Christian virtues and the divine charisms recommended to the pious devotion and imitation of the faithful. When we look at the lives of those who have faithfully followed Christ, we are inspired with a new reason for seeking the City that is to come and at the same time we are shown a most safe path by which among the vicissitudes of this world, in keeping with the state in life and condition proper to each of us, we will be able to arrive at perfect union with Christ, that is, perfect holiness. In the lives of those who, sharing in our humanity, are however more perfectly transformed into the image of Christ, God vividly manifests His presence and His face to men. He speaks to us in them, and gives us a sign of His Kingdom, to which we are strongly drawn, having so great a cloud of witnesses over us and such a witness to the truth of the Gospel. Nor is it by the title of example only that we cherish the memory of those in heaven, but still more in order that the union of the whole Church may be strengthened in the Spirit by the practice of fraternal charity. For just as Christian communion among wayfarers brings us closer to Christ, so our companionship with the saints joins us to Christ, from Whom as from its Fountain and Head issues every grace and the very life of the people of God. It is supremely fitting, therefore, that we love those friends and coheirs of Jesus Christ, who are also our brothers and extraordinary benefactors, that we render due thanks to God for them and "suppliantly invoke them and have recourse to their prayers, their power and help in obtaining benefits from God through His Son, Jesus Christ, who is our Redeemer and Saviour." For every genuine testimony of love shown by us to those in heaven, by its very nature tends toward and terminates in Christ who is the "crown of all saints," and through Him, in God Who is wonderful in his saints and is magnified in them. Our union with the Church in heaven is put into effect in its noblest manner especially in the sacred Liturgy, wherein the power of the Holy Spirit acts upon us through sacramental signs. Then, with combined rejoicing we celebrate together the praise of the divine majesty; then all those from every tribe and tongue and people and nation who have been redeemed by the blood of Christ and gathered together into one Church, with one song of praise magnify the one and triune God. Celebrating the Eucharistic sacrifice therefore, we are most closely united to the Church in heaven in communion with and venerating the memory first of all of the glorious ever-Virgin Mary, of Blessed Joseph and the blessed apostles and martyrs and of all the saints.