Fourth reason: conformity to the law of nature belongs to pure nature, so the righteousness that makes it possible is natural
Add that it belongs to the endowments of nature in a rational creature that is not corrupt but pure to conform to the law of nature and shape itself by its rules. So whatever it needs in order to conform to the law of nature and bring all its impulses under it does not go beyond the endowments and order of nature.
But a man without any righteousness or holiness, and subject to the weaknesses we are born with today, cannot shape himself by the law of nature. So the holiness and righteousness that remove such weaknesses must be counted among the gifts of uncorrupted nature.
Latin
LV. Adde quod ad naturae dotes in creatura rationali non corrupta sed pura pertinet, ut conformis sit legi naturae, & ad illius regulas se componat. Ac proinde quicquid sine quo non potest naturae legi sese conformare, & omnes motus suos illi subdere, dotes & ordinem naturae non excedit. Ad legem autem naturae se componere non potest, homo destitutus omni justitia & sanctitate, & infirmitatibus illis quibuscum hodie nascimur, obnoxius. Adeoque sanctitas & justitia illa, per quam tolluntur tales infirmitates, ad naturae non corruptae dona spectare censenda est.