11 As for some other objections which are advanced against this opinion, I think that I could easily dispose of them. For example, some think that they urge a conclusive argument against this opinion when they ask, how God finished all His works on the sixth day and rested on the seventh day, if He is still creating new souls. If we meet them with the quotation from the gospel (given by you in the letter to Marcellinus already mentioned), “My Father works hitherto,” they answer that He “works” in maintaining those natures which He has created, not in creating new natures; otherwise, this statement would contradict the words of Scripture in Genesis, where it is most plainly declared that God finished all His works. Moreover, the words of Scripture, that He rested, are unquestionably to be understood of His resting from creating new creatures, not from governing those which He had created; for at that time He made things which previously did not exist, and from making these He rested because He had finished all the creatures which before they existed He saw necessary to be created, so that thenceforward He did not create and make things which previously did not exist, but made and fashioned out of things already existing whatever He did make. Thus the statements, “He rested from His works,” and, “He works hitherto,” are both true, for the gospel could not contradict Genesis.
12. When, however, these things are brought forward by persons who advance them as conclusive against the opinion that God now creates new souls as He created the soul of the first man, and who hold either that He forms them from that one soul which existed before He rested from creation, or that He now sends them forth into bodies from some reservoir or storehouse of souls which He then created, it is easy to turn aside their argument by answering, that even in the six days God formed many things out of those natures which He had already created, as, for example, the birds and fishes were formed from the waters, and the trees, the grass, and the animals from the earth, and yet it is undeniable that He was then making things which did not exist before. For there existed previously no bird, no fish, no tree, no animal, and it is clearly understood that He rested from creating those things which previously were not, and were then created, that is to say, He ceased in this sense, that, after that, nothing was made by Him which did not already exist. But if, rejecting the opinions of all who believe either that God sends forth into men souls existing already in some incomprehensible reservoir, or that He makes souls emanate like drops of dew from Himself as particles of His own substance, or that He brings them forth from that one soul of the first man, or that He binds them in the fetters of the bodily members because of sins committed in a prior state of existence, if, I say, rejecting these, we affirm that for each individual He creates separately a new soul when he is born, we do not herein affirm that He makes anything which he had not already made. For He had already made man after His own image on the sixth day; and this work of His is unquestionably to be understood with reference to the rational soul of man. The same work He still does, not in creating what did not exist, but in multiplying what already existed. Wherefore it is true, on the one hand, that He rested from creating things which previously did not exist, and equally true, on the other hand, that He continues still to work, not only in governing what He has made, but also in making (not anything which did not previously exist, but) a larger number of those creatures which He had already made. Wherefore, either by such an explanation, or by any other which may seem better, we escape from the objection advanced by those who would make the fact that God rested from His works a conclusive argument against our believing that new souls are still being daily created, not from the first soul, but in the same manner as it was made.
13. Again, as for another objection, stated in the question, “Wherefore does He create souls for those whom He knows to be destined to an early death?” we may reply, that by the death of the children the sins of the parents are either reproved or chastised. We may, moreover, with all propriety, leave these things to the disposal of the Lord of all, for we know that he appoints to the succession of events in time, and therefore to the births and deaths of living creatures as included in these, a course which is consummate in beauty and perfect in the arrangement of all its parts; whereas we are not capable of perceiving those things by the perception of which, if it were attainable, we should be soothed with an ineffable, tranquil joy. For not in vain has the prophet, taught by divine inspiration, declared concerning God, “He brings forth in measured harmonies the course of time.” For which reason music, the science or capacity of correct harmony, has been given also by the kindness of God to mortals having reasonable souls, with a view to keep them in mind of this great truth. For if a man, when composing a song which is to suit a particular melody, knows how to distribute the length of time allowed to each word so as to make the song flow and pass on in most beautiful adaptation to the ever-changing notes of the melody, how much more shall God, whose wisdom is to be esteemed as infinitely transcending human arts, make infallible provision that not one of the spaces of time alloted to natures that are born and die— spaces which are like the words and syllables of the successive epochs of the course of time— shall have, in what we may call the sublime psalm of the vicissitudes of this world, a duration either more brief or more protracted than the foreknown and predetermined harmony requires! For when I may speak thus with reference even to the leaves of every tree, and the number of the hairs upon our heads, how much more may I say it regarding the birth and death of men, seeing that every man's life on earth continues for a time, which is neither longer nor shorter than God knows to be in harmony with the plan according to which He rules the universe.
14. As to the assertion that everything which has begun to exist in time is incapable of immortality, because all things which are born die, and all things which have grown decay through age, and the opinion which they affirm to follow necessarily from this, viz. that the soul of man must owe its immortality to its having been created before time began, this does not disturb my faith; for, passing over other examples, which conclusively dispose of this assertion, I need only refer to the body of Christ, which now “dies no more; death shall have no more dominion over it.”
Source: Letters (New Advent)