Part I: Ecclesiology. Basic observations on the subject of changeable and unchangeable factors in th Church. The faith of the Christian and the doctrine of the Church does the Church offer any ultimate certainties? On the concept of infallibility in Catholic theology. Part II: Questions in the Church. What is a sacrament? Introductory observations on Thomas Aquinas theology of the sacraments in general considerations on the active role of the person in the sacrament event. Part III: The Church in the World. Some problems in contemporary ecumenism. Ecumenical theology in the future the unreadiness of the Church members to accept poverty.