Sun and Moon allegory

By doing so, it illustrates that the Roman Catholic Pope, as "Supreme Pontiff", "Vicar of Christ", et cetera, and therefore the supreme universal spiritual authority on Earth, is like the Sun that is the one source of light for itself and all other celestial bodies orbiting it; while the Holy Roman Emperor, as symbolic and intended supreme civil, political, and secular authority on Earth, and having theoretically received his authority from and at the pleasure of the Pope, is like the Moon – that is, dependent upon the Sun for any illumination, merely reflects solar light, and ultimately has no light without the Sun.

[1] It is related to the general theory of Papal supremacy and "plenitudo potestatis" as articulated by the Roman Catholic Church.

Just as God, founder of the universe, has constituted two large luminaries in the firmament of Heaven, a major one to dominate the day and a minor one to dominate the night, so he has established in the firmament of the Universal Church, which is signified by the name of Heaven, two great dignities, a major one to preside--so to speak--over the days of the souls, and a minor one to preside over the nights of the bodies.

If he refuses to make satisfaction within a year, let the matter be made known to the supreme pontiff, that he may declare the ruler's vassals absolved from their allegiance and may offer the territory to be ruled by Catholics, who on the extermination of the heretics may possess it without hindrance and preserve it in the purity of faith; the right, however, of the chief ruler is to be respected as long as he offers no obstacle in this matter and permits freedom of action.

[3]While this theory of papal sovereignty in temporal as well as spiritual matters was, by the fourteenth century, generally rejected as out-of-date,[4] it entered into canon law and was reinforced by the Allegory of the Two Swords in the bull of Pope Boniface VIII entitled Unam Sanctam.