In the composition of the mass, Beethoven was on familiar ground; the work was congenial to him.  The emotions called up by the subject swayed him to such an extent that he had difficulty in keeping it within bounds.  The mass was a form of music with which he had been associated from childhood.  It will be remembered that he played the organ at the age of twelve years at church services, a practice which was kept up for some years.  His earliest impressions on the subject of music were in this style.  He was, in addition, inclined to it by temperament.

The beautiful text appealed to him strongly.  It is related that when the German version of his first Mass (in C) was brought him, he quickly opened the manuscript and ran over a few pages.  When he came to the Qui tollis, the tears trickled from his eyes and he was obliged to desist, saying with the deepest emotion, “Yes, that was precisely my feeling when I composed it.”

His journal entries at the time of beginning work on the Mass in D show how completely the subject had taken possession of him.  “To compose true religious music, consult the old chorals in use in monasteries,” he wrote, which gives the clew to his frequent lapses into the ancient ecclesiastical modes, the Lydian and Dorian, in this mass, a practice for which Bach furnished a precedent.  “Drop operas and everything else, write only in your own style,” is another entry of this time, showing his predilection for church music.

The summer of 1818 was spent at Moedling.  He was in the best of health and spirits as stated, and began the work with great energy and enthusiasm.  His whole nature seemed to change, Schindler states, when he began the great work.  His interest and absorption in it was extraordinary, as is shown by the sketch-books from the beginning.  Enthusiasm carried him on to the consummation of a greater work than any he had yet accomplished.  Hitherto, every achievement was merely a resting-place up the mountainside, the prospect acting as a spur to him to go yet higher, well knowing what Emerson finely stated, and was putting into practice at this very time, that new gifts will be supplied in proportion as we make use of those we have. Dem Muthigen hilft Gott! said Schiller.  Beethoven seemed to have some prevision that only a few more years would be allotted him for work; when he began on the mass his inspiration was like a river that had broken its bounds.  Every nerve and fibre of his being called him to his work.  He was like a war-horse that scents the battle.  He now abandoned himself more than ever to the impulse for creating.  For the next few years he lived the abstracted life of the enthusiast to whom every-day concerns are but incidental and unimportant things, and his art the one great matter.  The gigantic tone-pictures which were constantly forming themselves in his inner consciousness were of so much greater importance than the events of his external life, that the latter were dwarfed by comparison and lost their significance.  He now made a greater surrender of the ties connecting him with every-day life than ever before.  His industry was phenomenal, but it soon became apparent that the work would not be ready for the Installation, the date of which was set for March 20, 1820.  It was in reality not completed until nearly two years after this event.