In the cosmology and theology of Pierre Teilhard de Chardin, the Church has not often been considered to possess any significant function. In fact, Teilhard devotes considerable attention to several key ecclesiological questions. Fundamental to the Christian mission of the conversion of the world to Christ is an incarnational theology of the conversion of the Church to the world. This requires the Church to accept the modern world as currently and contingently constituted. The Church spiritually transforms the materiality of the world in its sacraments and through the practical works of its members. It provides the physical means of the convergence of the world towards its final unity, and for this reason calls its members to obedience, despite its imperfections. Catholicism has the potential to bring all Christians to unity in a self-transforming ecumenism that could also encompass other faiths.