But he who culls what is useful for the advantage of the catechumens, and especially when they are Greeks (and the earth is the Lord’s, and the fulness thereof[1050]), must not abstain from erudition, like irrational animals; but he must collect as many aids as possible for his hearers. But he must by no means linger over these studies, except solely for the advantage accruing from them; so that, on grasping and obtaining this, he may be able to take his departure home to the true philosophy, which is a strong cable for the soul, providing security from everything. Music is then to be handled for the sake of the embellishment and composure of manners. For instance, at a banquet we pledge each other while the music is playing;[1051] soothing by song the eagerness of our desires, and glorifying God for the copious gift of human enjoyments, for His perpetual supply of the food necessary for the growth of the body and of the soul. But we must reject superfluous music, which enervates men’s souls, and leads to variety,--now mournful, and then licentious and voluptuous, and then frenzied and frantic. The same holds also of astronomy. For treating of the description of the celestial objects, about the form of the universe, and the revolution of the heavens, and the motion of the stars, leading the soul nearer to the creative power, it teaches to quickness in perceiving the seasons of the year, the changes of the air, and the appearance of the stars; since also navigation and husbandry derive from this much benefit, as architecture and building from geometry. This branch of learning, too, makes the soul in the highest degree observant, capable of perceiving the true and detecting the false, of discovering correspondences and proportions, so as to hunt out for similarity in things dissimilar; and conducts us to the discovery of length without breadth, and superficial extent without thickness, and an indivisible point, and transports to intellectual objects from those of sense. The studies of philosophy, therefore, and philosophy itself, are aids in treating of the truth. For instance, the cloak was once a fleece; then it was shorn, and became warp and woof; and then it was woven. Accordingly the soul must be prepared and variously exercised, if it would become in the highest degree good. For there is the scientific and the practical element in truth; and the latter flows from the speculative; and there is need of great practice, and exercise, and experience. But in speculation, one element relates to one’s neighbours and another to one’s self. Wherefore also training ought to be so moulded as to be adapted to both. He, then, who has acquired a competent acquaintance with the subjects which embrace the principles which conduce to scientific knowledge (_gnosis_), may stop and remain for the future in quiet, directing his actions in conformity with his theory.