This article examines the theological basis of the divergence that still separates the Roman Catholic Church from the churches of the Reformation. It offers a diagnosis of this issue by following a triangular circuit made up of three poles in constant intercommunication: ecclesiology, soteriology and anthropology. In ecclesiology, the concept of the Church as sacrament (mystery) - even if it is debated - makes it possible to situate the difficulty concerning the instrumentality of the Church and ultimately its service of the unique mediation of Christ. Protestant categories point to a break in the sacramental nature of the Church (res et sacramentum, in Augustinian language) between reality (res tantum) and the visible sign (sacramentum tantum). Soteriology manifests a Protestant underestimation of the action of Christ's free humanity in the work of salvation, the consequence rather than the cause of an overly one-sided conception of justification in its effects. Theological anthropology, the conception of the relationship between sinful man and God, and the difficulty concerning analogy (which is still evolving) are perhaps the final source of the divergence.