Commentary
In the verses cited above, first it was declared that the alternation of night and day was a sign of the most perfect power of Allah Ta` ala. Then it was said that there was great wisdom in the making of the night dark and the day, bright. As for the wise consideration behind the making of the night dark, it was not mentioned at this place. It has, however, been mentioned in other verses that the darkness of the night is appropriate and conducive to sleep and rest. The divine arrangement is such that humans and animals go to sleep in the darkness of that very night. In fact, the whole world sleeps simultaneously in harmony with its night. Had different people been scheduled to sleep at different timings, the noises made by those awake and those working at jobs would have turned the sleep of the sleeping into a nightmare.
As for the day being bright, it has two elements of wisdom. Firstly, one can earn his living in the light of the day and natural light is needed for jobs, businesses and industries. Secondly, the alternation of night and day helps one know the number of years, for instance, the completion of three hundred and sixty days tells us that a full year has gone by.
Similarly, other calculations are also related to the alternation of night and day. If this variation of night and day were not there, it would have been difficult to fix the wages of the wage earner, the employment of the employee and the time duration of transactions.