XVII. (53) The aforesaid number therefore being accounted worthy of such pre-eminence in nature, the Creator of necessity adorned the heaven by the number four, namely by that most beautiful and most godlike ornament the lightgiving stars. And knowing that of all existing things light is the most excellent, he made it the instrument of the best of all the senses, sight. For what the mind is in the soul, that the eye is in the body. For each of them sees, the one beholding those existing things which are perceptible only to the intellect, and the other those which are perceptible to the external senses. But the mind is in need of knowledge in order to distinguish incorporeal things, and the eyes have need of light in order to be able to perceive bodies, and light is also the cause of many other good things to men, and particularly of the greatest, namely philosophy. (54) For the sight being sent upwards by light and beholding the nature of the stars and their harmonious movement, and the well-ordered revolutions of the fixed stars, and of the planets, some always revolving in the same manner and coming to the same places, and others having double periods in an anomalous and somewhat contrary manner, beholding also, the harmonious dances of all these bodies arranged according to the laws of perfect music, causes an ineffable joy and delight to the soul. And the soul, feasting on a continuous series of spectacles, for one succeeds another, has an insatiable love for beholding such. Then, as is usually the case, it examines with increased curiosity what is the substance of these things which are visible; and whether they have an existence without having been created, or whether they received their origin by creation, and what is the character of their movement, and what the causes are by which everything is regulated. And it is from inquiries into these things that philosophy has arisen, than which no more perfect good has entered into human life.