Catechism of the Catholic Church

772 It is in the Church that Christ fulfills and reveals his own mystery as the purpose of God's plan: "to unite all things in him." ¹⁸⁹ St. Paul calls the nuptial union of Christ and the Church "a great mystery." Because she is united to Christ as to her bridegroom, she becomes a mystery in her turn. ¹⁹⁰ Contemplating this mystery in her, Paul exclaims: "Christ in you, the hope of glory." ¹⁹¹

773 In the Church this communion of men with God, in the "love [that] never ends," is the purpose which governs everything in her that is a sacramental means, tied to this passing world. ¹⁹²

"[The Church's] structure is totally ordered to the holiness of Christ's members. And holiness is measured according to the 'great mystery' in which the Bride responds with the gift of love to the gift of the Bridegroom." ¹⁹³ Mary goes before us all in the holiness that is the Church's mystery as "the bride without spot or wrinkle." ¹⁹⁴ This is why the "Marian" dimension of the Church precedes the "Petrine." ¹⁹⁵