Among the various theories about parallel organum, some are quite extravagant. Here is an attempt to explain the relationship between architecture and music during that era. It is important to note that the resonances of fourths and fifths are closely linked to the architecture of Gothic churches—these "celestial caves."
For any musician with a free spirit and creative mind, the temptation to sing in fifths or fourths is exhilarating, as these intervals persist within the church vaults. They intertwine without creating saturation or leaving dissonant traces.
Sustained notes sung within these architectural spaces produce a synesthetic experience of sound and light in the human body. This aligns with the ultimate purpose of such music: the illumination of the spirit, calling the congregation to faith—much like the mantras of Hindu religious culture, which aim at transcendence.
Unlike Hindu traditions, where individuals must produce the sounds themselves to attain inner peace, in the case of parallel organum, it is the singers who lead the congregation into a spiritual trance.
The question remains: was this phenomenon purely accidental, emerging from musical intuition and practice, gradually shaping a style that resonated with the architecture? Or was this art based on cosmogonic knowledge—now lost—passed down only through oral tradition? Perhaps these secrets remain encoded in ancient manuscripts, yet to be brought to light.