The author draws some methodolical lines for grasping exactly Luther’s understanding of the Mass as an «expiatory-propitiatory» sacrifice and his reasons for refusing it. Using just Luther’s eucharistic writings or the Ausburg confession, claims the author, is not enough for having a complete picture of his eucharistic theology. For interpreting these writings it is necessary to take into account his overall theology. The author underlines the difficulties of such an endeavour, for Luther is in no way systematic. On these premises, he wonders whether it is possible to have a precise knowledge of Luther’s positions on the topic. Nevertheless in his view these difficulties can be overcome by remembering that Luther feels compelled to synthetize all of his thought under one heading: justification by faith alone. The author thinks that this point is the hermeneutical key of the Reformer’s overall thought, and then of his eucharistic theology. Another article is being prepared on this topic (pp. 211-231).