On Counter Promises
6 We are therefore to suppose that the saints will remain there until they recognise the twofold mode of government in those things which are performed in the air. And when I say “twofold mode,” I mean this: When we were upon earth, we saw either animals or trees, and beheld the differences among them, and also the very great diversity among men; but although we saw these things, we did not understand the reason of them; and this only was suggested to us from the visible diversity, that we should examine and inquire upon what principle these things were either created or diversely arranged. And a zeal or desire for knowledge of this kind being conceived by us on earth, the full understanding and comprehension of it will be granted after death, if indeed the result should follow according to our expectations. When, therefore, we shall have fully comprehended its nature, we shall understand in a twofold manner what we saw on earth. Some such view, then, must we hold regarding this abode in the air. I think, therefore, that all the saints who depart from this life will remain in some place situated on the earth, which holy Scripture calls paradise, as in some place of instruction, and, so to speak, class-room or school of souls, in which they are to be instructed regarding all the things which they had seen on earth, and are to receive also some information respecting things that are to follow in the future, as even when in this life they had obtained in some degree indications of future events, although “through a glass darkly,” all of which are revealed more clearly and distinctly to the saints in their proper time and place. If any one indeed be pure in heart, and holy in mind, and more practised in perception, he will, by making more rapid progress, quickly ascend to a place in the air, and reach the kingdom of heaven, through those mansions, so to speak, in the various places which the Greeks have termed spheres, i.e., globes, but which holy Scripture has called heavens; in each of which he will first see clearly what is done there, and in the second place, will discover the reason why things are so done: and thus he will in order pass through all gradations, following Him who has passed into the heavens, Jesus the Son of God, who said, “I will that where I am, these may be also.” And of this diversity of places He speaks, when He says, “In My Father's house are many mansions.” He Himself is everywhere, and passes swiftly through all things; nor are we any longer to understand Him as existing in those narrow limits in which He was once confined for our sakes, i.e., not in that circumscribed body which He occupied on earth, when dwelling among men, according to which He might be considered as enclosed in some one place.
7. When, then, the saints shall have reached the celestial abodes, they will clearly see the nature of the stars one by one, and will understand whether they are endued with life, or their condition, whatever it is. And they will comprehend also the other reasons for the works of God, which He Himself will reveal to them. For He will show to them, as to children, the causes of things and the power of His creation, and will explain why that star was placed in that particular quarter of the sky, and why it was separated from another by so great an intervening space; what, e.g., would have been the consequence if it had been nearer or more remote; or if that star had been larger than this, how the totality of things would not have remained the same, but all would have been transformed into a different condition of being. And so, when they have finished all those matters which are connected with the stars, and with the heavenly revolutions, they will come to those which are not seen, or to those whose names only we have heard, and to things which are invisible, which the Apostle Paul has informed us are numerous, although what they are, or what difference may exist among them, we cannot even conjecture by our feeble intellect. And thus the rational nature, growing by each individual step, not as it grew in this life in flesh, and body, and soul, but enlarged in understanding and in power of perception, is raised as a mind already perfect to perfect knowledge, no longer at all impeded by those carnal senses, but increased in intellectual growth; and ever gazing purely, and, so to speak, face to face, on the causes of things, it attains perfection, firstly, viz., that by which it ascends to (the truth), and secondly, that by which it abides in it, having problems and the understanding of things, and the causes of events, as the food on which it may feast. For as in this life our bodies grow physically to what they are, through a sufficiency of food in early life supplying the means of increase, but after the due height has been attained we use food no longer to grow, but to live, and to be preserved in life by it; so also I think that the mind, when it has attained perfection, eats and avails itself of suitable and appropriate food in such a degree, that nothing ought to be either deficient or superfluous. And in all things this food is to be understood as the contemplation and understanding of God, which is of a measure appropriate and suitable to this nature, which was made and created; and this measure it is proper should be observed by every one of those who are beginning to see God, i.e., to understand Him through purity of heart.
Source: De Principiis (New Advent)