The popular idea of a Christian universe corrupted in its very nature by sin owes much of its favour to the influence of Luther, Calvin and Jensenius; but to look at Christianity through their eyes would be to regard it in a very different light than that of Thomism, or even of authentic Augustinianism. No one, in fact could be further thatn St. Augustine from considering the world in the state of fallen nature as worthless. His own metaphysical principles would firbit it, to start with. Since evil is but the corruption of a good and cannot possibly subsist at all save in this good, it follows that inasmuch as there is evil, there is a good. [p. 122]
* * *... the good of nature is a real part of nature, and is not therefore to be suppressed, but simply diminished by sin. Every act initiates a habit, that is to tsay the first bad act results in a disposition to commit others and thus enfeebles the natural human inclination towards good. But this inclination, nevertheless, remains, and so the way to the acquisition of all the virtues remains open. As for the first and proper sense of the word "nature", that is to say the very sense of man, it can neither be suppressed nor diminished by sin; primum igitur bonum naturae, nec tollitur, nec diminuitur per peccatum. To deny this would be to suppose that at one ad the same time man could both remain man and cease to be man. Thus sin neither adds to nor takes away from human nature: ea enim quae sunt naturalia homini, neque subtrahuntur neque dantur homini per peccatum. Man's metaphysical status is essentially unchangeable and independent of all the accidents that may befall him. [p. 124-125].
Etienne Gilson, Spirit of Medieval Philosophy