The seasons follow the ordered motion of the lights

But the most foolish of all are those who labor at the crafts. The farmer will prosper, they say, without sowing seed or sharpening a sickle, and the merchant will become exceedingly rich whether he wants to or not, because fate gathers wealth for him. Our great Christian hopes will vanish into nothing, since righteousness is not honored and sin is not condemned, because nothing is accomplished by human choice. For where necessity and fate rule, there is no place for what is deserved, which is the special mark of just judgment. So much for those people. You do not need more words from me, since you are sound in your own thinking, and the time does not allow me to stretch out my response to them beyond measure.

Let us return to the next words of the text. "Let them be for signs and for seasons and for days and for years," it says (Genesis 1:14). We have already spoken about the signs. By seasons, I think he means the alternations of the year's periods: winter, spring, summer, and autumn. The ordered movement of the lights causes us to pass through these in good order. Winter comes when the sun lingers in the southern regions and produces a long stretch of nighttime shadow over our part of the earth, so that the air around the earth grows cold, and all the moist vapors gather around us and bring about rain, frost, and boundless snow. But when the sun returns again from the southern regions and reaches the midpoint, so that it divides the time equally between night and day, the more it lingers over the places above the earth, the more it gradually brings back a mild temperature. Then spring comes, which is the beginning of sprouting for all plants, grants renewal of life to most trees, and preserves the race of all land and water creatures through the succession of their offspring. From there the sun drives on toward the summer solstice, toward the Bear itself, and brings about the longest days for us. Because it stays in contact with the air for the greatest length of time, it scorches the air above our heads and dries out the whole earth, and in this way it helps the seeds to mature and urges the fruits of the trees toward ripeness. At that time the sun is at its most blazing, making the shadows short at midday, because it shines down on our region from on high. The longest days are those in which the shadows are shortest, and the shortest days are those in which the shadows are longest. This is true for us who are called different-shadowed, all of us who inhabit the northern parts of the earth. For there are already some people who, for two days of the whole year, become completely shadowless at midday. The sun shines down on them from directly overhead and illuminates them equally from every side, so that even the water in deep wells is lit up through their narrow openings. That is why some call them shadowless. But those beyond the spice-bearing land cast their shadows alternately to both sides. They are the only ones in our inhabited world who send their shadows toward the south at midday. That is why some have named them double-shadowed.