Starting from the way in which Vatican II combines references to the Church as Body of Christ and Bride of Christ in Lumen Gentium 7, this paper explores the relationship between these two images, both of which are centred on the Eucharist which in fact is their point of contact and union. The free consent of the Bride to the nuptial union is summarised in Mary's fiat at the Annunciation and reiterated at the foot of the Cross. In its response to Christ, the Church is fundamentally Marian, and will always remain so, into eternity. In this life, however, the Church has a sacramental and hierarchical structure by which Christ comes to encounter his Bride so as then, in her, to bring salvation to the world. She is the intrinsic medium of the salvific event of Christ, making him present to human freedom. Peter exemplifies the structure and ministry of the Church in its objectivity, and the Petrine principle is rooted in the Marian principle, both being co-extensive with the Church. An understanding of the Church in these terms, endorsed by Pope John Paul II, originated with Hans Urs von Balthasar, who, however, did not fully expound it. This paper argues for the close integration of ecclesiology and Mariology. Furthermore, it proposes that the nuptial mystery can be a key towards synthesising the Marian and Petrine dimensions of the Church, and thereby understanding the Church in all aspects of its structure and life. From this standpoint, fresh light is cast upon burning pastoral questions such as the (non-)ordination of women and the celibacy of the clergy.