98 As the vastness of the charity with which Christ loved His Church is equalled by its constant activity, we all, with the same assiduous and zealous charity must love the Mystical Body of Christ. Now from the moment of His Incarnation, when he laid the first foundations of the Church, even to His last mortal breath, our Redeemer never ceased for an instant, though He was the Son of God, to labor unto weariness in order to establish and strengthen His Church, whether by giving us the shining example of His holiness, or by preaching, or conversing, or gathering and instructing disciples. And so We desire that all who claim the Church as their mother, should seriously consider that not only the clergy and those who have consecrated themselves to God in the religious life, but the other members of the Mystical Body of Jesus Christ as well have, each in his degree, the obligation of working hard and constantly for the building up and increase of this Body. We wish this to be borne in mind especially by members of Catholic Action who assist the Bishops and the priests in their apostolic labours - and to their praise be it said, they do realize it - and also by those members of pious associations which work for the same end. There is no one who does not realize their energetic zeal is of the highest importance and of the greatest weight especially in the present circumstances.
Source: Mystici Corporis Christi (Vatican.va)