37 But if souls were, as is said, the Lord's children, and begotten by the Supreme Power, nothing would have been wanting to make them perfect, as they would have been born with the most perfect excellence: they would all have had one mind, and been of one accord; they would always dwell in the royal palace; and would not, passing by the seats of bliss in which they had learned and kept in mind the noblest teachings, rashly seek these regions of earth, that they might live enclosed in gloomy bodies amid phlegm and blood, among these bags of filth and most disgusting vessels of urine.
But, an opponent will say, it was necessary that these parts too should be peopled, and therefore Almighty God sent souls hither to form some colonies, as it were. And of what use are men to the world, and on account of what are they necessary, so that they may not be believed to have been destined to live here and be the tenants of an earthly body for no purpose? They have a share, my opponent says, in perfecting the completeness of this immense mass, and without their addition this whole universe is incomplete and imperfect.
What then? If there were not men, would the world cease to discharge its functions? Would the stars not go through their changes? Would there not be summers and winters? Would the blasts of the winds be lulled? And from the clouds gathered and hanging overhead would not the showers come down upon the earth to temper droughts? But now all things must go on in their own courses, and not give up following the arrangement established by nature, even if there should be no name of man heard in the world, and this earth should be still with the silence of an unpeopled desert.
How then is it alleged that it was necessary that an inhabitant should be given to these regions, since it is clear that by man comes nothing to aid in perfecting the world, and that all his exertions regard his private convenience always, and never cease to aim at his own advantage?
Source: Against the Heathen (New Advent)