The moon's changing shapes teach human mutability

Its fiery quality is so measured that it neither burns up the earth through excess nor leaves it frozen and barren through deficiency. And what has been said about the sun should be understood as applying in kind to the moon as well. For its body is also great, and it is the brightest light after the sun. Yet its size does not remain always visible. At one time it appears completed in its circle, at another lacking and diminished, showing its missing part on one side or another. For as it waxes, one part of it is shadowed, and at the time of its waning another part is hidden. There is some inexpressible design of the wise craftsman in this varied alternation of shapes. It is as though he were giving us a clear example of our own nature: that nothing human is stable, but some things proceed from non-being into perfection, while others, after reaching their proper prime and growing to their fullest measure, waste away and perish again through gradual subtractions, and as they diminish they are brought low. So from the sight of the moon we are taught about our own condition, and by taking thought of the swift turning of human affairs we learn not to think highly of life's successes, not to exult in positions of power, not to be lifted up by the uncertainty of wealth, to despise the flesh around which change revolves, and to care for the soul whose good is unshaken. If the moon troubles you as it gradually consumes its light through subtractions, let a soul trouble you more—a soul that has acquired virtue and then through carelessness destroys what is good, never remaining in the same disposition but constantly turning and shifting because of the instability of its purpose. For truly, as it is said, "The fool changes like the moon" (Sirach 27:11). I think too that the change of the moon contributes no small benefit to the constitution of living creatures and to the other things that grow from the earth. Bodies are disposed differently when the moon wanes and when it waxes: when it is declining they become porous and empty, and when it is waxing and hastening toward fullness they are filled up again, because the moon secretly sends down a certain moisture mixed with warmth that reaches into the depths. Those who sleep under the moon show this, as the spaces of their heads are filled with excess moisture; so do freshly slaughtered meats, which quickly turn at the touch of the moon, and the brains of animals, and the moistest parts of sea creatures, and the piths of trees. All these things the moon could not have power to change along with its own alteration unless it were something extraordinary and surpassing in power, according to the testimony of Scripture. And the conditions of the air are also affected along with the moon's changes, as the sudden disturbances at the new moon bear witness to us—when calm and stillness often give way to turmoil, clouds shaken and colliding with one another—and the backflows in the straits, and the ebb tide around what is called the ocean, which those who live nearby have discovered follows the cycles of the moon in an orderly way. For the straits flow back and forth in either direction according to the remaining phases of the moon, but at the time of its birth they do not remain still even for the briefest moment; they are in constant surge and swaying until the moon appears again and gives a certain regularity to the backflow.