On the most famous of all Beethoven portraits, the oil painting by Joseph Stieler from 1820, the composer holds the score of the Missa Solemnis in his hands. This is no coincidence since Beethoven considered it his "greatest work". "From the heart - may it go again - to the heart" is the sentence he uttered when he presented the piece. Beethoven thus concluded a work that had taken him four years to complete. His intention was not to contribute to the Catholic liturgy with another interchangeable work but to deliver a personal confession of faith, "true church music", as he put it in 1818. Beethoven's contemporaries and successors found it difficult to share such high aspirations. At the partial premiere in Vienna in 1824, the Missa Solemnis was clearly overshadowed by the 9th Symphony, which was also a new work. Among later listeners of the mass, approval and rejection were balanced. For some, the composer had given his best in this work, whereas others felt a "lack of unity". To this day, the op. 123 probably remains one of Beethoven's most controversial major works. It all began quite harmlessly. In 1819, the Archbishop of Olomouc died; Archduke Rudolph, the Emperor's younger brother and Beethoven's composition pupil was named as his successor. Beethoven, who had already dedicated a whole series of works to his patron and was hoping to obtain a position as Kapellmeister, offered to contribute to the enthronement feast with a solemn mass. However, only two of the five movements were available at the time of the celebration, in March 1820, the project having grown out of control. It was not until three years later that the complete score was handed over to the dedicatee. There are many reasons for this delay. On the one hand, Beethoven made extensive preparations for the setting of this mass. He not only had the Latin text of the liturgy translated but also studied the music of the Middle Ages and the Renaissance, as well as theological and philosophical texts. This care proves the extent to which the composer intended to deliver a work able to set standards, one of personal and general significance. Beethoven also broke new ground formally. Instead of dividing the text of the mass text into many small "numbers" - choruses, arias, ensembles - as Bach, Haydn and Mozart had done, he limited himself to the five sections given by the liturgy: Kyrie, Gloria, Credo, Sanctus and Agnus Dei. Within each of these sections, however, the expression changes frequently depending on the text, as do the and tempo, key, metre and instrumentation. The result is a panoramic-like painting of great dynamic and visual power, the intensity of which of course overwhelmed many listeners. Nothing here is accidental, everything is subordinated to the overall context. Beethoven's was also innovative in the way he related old and new, tradition and modernity. The fugues and old-fashioned harmonies of the Missa Solemnis stand on equal footing with symphonic orchestral treatment and unusual chord progressions. Conventional interpretations of the text exist alongside expressive treatment of the timbres. The "transformation music", a purely instrumental prelude that Beethoven placed before the Benedictus, is one of the most distinctive moments of this work. Perhaps what is fascinating about the Missa Solemnis, at least from today's perspective, is the intertwining of faith and doubt, this highly individual approach to the phenomenon of religiousness. Beethoven's music offers space for questions, longing and despair as well as for jubilation, confidence and strength. After all, the 50-year-old composer was himself in an ambivalent situation: admired as a musician, he experienced failure in his private life. In any case, his "greatest work" leaves no one indifferent.