Nor is the fall hard to explain if rectitude was natural: the higher part turned from God, and disorder followed. De Justitia Primi Hominis closes
Nor, granting that the rectitude created with man was itself natural and not supernatural, is it as hard as Bellarmine thinks to show how the corruption now in us, which forces reason to be subject to the passions, got into human nature.
That flaw began in the higher part of the soul, when it turned away from God and began to be carried toward the object of the sense appetite as though that were its end. The disorder (ataxia) of man's moral faculties followed from that. Their original rectitude lay in all their impulses and affections being directed, at the command of mind and reason, toward God as their highest end. Reason cannot turn aside from that end and put earthly goods in its place without being forced to serve sense and appetite, shamefully and against its own nature, since their object now stands for it in place of the highest end.
Latin
LIX. Nec posito quod rectitudo homini concreata ipsa naturalis fuerit, non supernaturalis, ita difficile est, ut Bellarminus existimat, ostendere qua ratione corruptio illa quae jam nobis inest, & per quam ratio cogitur affectibus subesse, naturam humanam invasit. Vitium enim illud ortum habuit a parte animi superiore, quum a Deo discedens, ferri coepit in objectum appetitus sensitivi tanquam in finem suum. Nam inde secuta est facultatum moralium in homine ἀταξία. Siquidem primigenia earum rectitudo in eo consistebat quod ad Deum tanquam finem summum omnes illarum motus & affectus, ex mentis & rationis imperio, dirigebantur. A quo fine ratio deviare non potest, & bona terrena illi substituere, quin sensui & appetitui, quorum jam objectum pro fine summo est, turpiter, & contra propriam naturam servire cogatur.