Greetings Maurizio.
This is one of my favorite Masonic works by Mozart. Here is some info I have on this piece and I hope it'll help.
From "Mozart and the Masons" by H.C. Robbins Landon:
"Mozart's most important piece of Masonic music hitherto had originated in the deaths, within a day of each other in 1785, of two Brothers: Georg August, Duke of Mecklenburg-Strelitz (d. 6 Nov.), and Franz, Count Esterhazy of Galantha (d. 7 Nov.). In the Vienna Lodge ‘Zur gekroenten Hoffnung’ on 17 Nov. was held a Lodge of Sorrows. Wenzel Tobias Epstein delievered the Oration, while Mozart, with a collection of musicians, some of them Brethren, produced his Maurerische Trauermusik (K.477). This Masonic Funeral Music, with its heavy symbolism (concept of three), also in its overall form (in the middle B part there appears an old Gregorian chant, part of the music for Passion week), reveals Mozart's total involment with the theories and philosophies of death and their symbolic relationship to the First Degree of the Craft."
From Dr. B. Paumgartner:
"The Masonic Funeral Music holds a place all its own among Mozart's works, not only for its form and homogeneity, for the ingenious choice of the instruments and their exquisite technical treatment, but also through the unique grouping of a solemn march around the fundamental element of a gregorian chorale. Mozart very accurately penned the Cantus Firmus on a separate leaf in order to avoid errors in the elaboration. According to Heimsoeth the first five bars of this melody (bar 25-29) are identical with the first Psalm tone with the first Difference after the Cologne Antiphonary. What follows is a local compilation of several Psalm tones for the ‘Miserere mei Deus’ -- a Penitential psalm such as is frequently used for funerals in several places."
From "Mozart and Masonry" by Paul Nettl:
"Masonic music can be devided into three classes. The first consists of various songs and instrumental pieces which were composed for use at lodge meetings, dinners and other occasions. The second category comprises music which was not originally intended for Masonic occasions, but whose contents made it appropriate for such use. The third and highest group includes compositions which are intended to express the Masonic creed but are not for use in ceremonies."
Andrea Hubrich