In his fascinating book Die Zauberflöte, Oper und Mysterium (München-Wien, Carl Hanser Verlag, 2005; A varázsfuvola, opera és misztérium, Budapest, Atlantisz, 2012), Jan Assmann saw Mozart’s opera as a link between the Egyptian–Hellenistic mystery religions and the 18th-century Freemasonry and its legacy. According to his theory, Die Zauberflöte inherently contains an initiation ritual, which, in light of the Masonic interpretation of the mysteries, we can see as representing the ”lesser” and ”greater” stages of the masonic initiation. This study demonstrates that the musical intonation of the opera (the structure of tonalities, melody, harmony, rhythm and orchestration, etc.) leads finally even through three lines to the Nether World (Isis-Osiris/ Demeter-Persephone/ Orpheus-Euridice); yet in spite of all it may seem to be an absurd idea to connect Sarastro’s Empire with it. But the problem of rebirth in voluntary death-experience is not unfamiliar within Freemasonry, the intensive absorption in mortality is a part of their initiating processes. The ”secret” of Mozart’s ”masonic opera” is the summary of a mystical happiness got by insight into the last stage of masonic initiation.