Venerable Fulton Sheen once famously said that “There are not one hundred people in the United States who hate the Catholic Church, but there are millions who hate what they wrongly perceive the Catholic Church to be – which is, of course, quite a different thing.” What is the true understanding of the mystery of the Church? In Lumen Gentium, the Church famously identifies herself as the sacrament of salvation, and various attempts have been made at developing an ecclesiology rooted in this idea. Another approach, nevertheless, prominent in the opening chapter of Lumen Gentium, is the relation of the Church to the Trinity in light of the divine missions, especially those of the Incarnation and Pentecost. Trinitarian Ecclesiology is an example of this approach to the mystery of the Church that places the divine missions at the head and the heart of the work. The order of Journet's work is based on the four causes of the Church. Journet situates the treatise on the hierarchy in its proper place as belonging to the efficient cause of the Church in order to treat the more central mystery of the Church in her formal and material causes, namely the sanctifying gift of fully Christic charity and its visible manifestation. While Journet’s magisterial work may already be identified as a Trinitarian Ecclesiology, recent research into the Trinitarian theology of St. Thomas Aquinas has deepened our understanding of his teaching, particularly in the way that creatures can relate to the divine persons in the divine missions. With a clearer understanding of the relation of creatures to the divine persons rooted in grace and its effects, a deeper vision of the mystery of the Church emerges, one that sees the Church as the visible mission of the Holy Spirit, inseparably joined with the visible mission of the Son in the Incarnation. The Great Mystery of Christ and the Church is the unity of the visible missions of the Son and the Spirit who have been sent into the world for our salvation.