A precept kept as to substance can still be sin; or it can have a natural moral honesty
The doctors of the Roman Church further observe that those who keep the precepts as to the substance of the works, but not out of charity, still fall into two classes.
'A precept of the law,' they say, 'can be kept as to the substance of the work and still be kept with sin, so that the act should not be counted praiseworthy or honourable. This happens when someone acts from a corrupt desire and for a bad end: for instance, if he returns a deposit to a friend or gives something to the needy, but to please a harlot and serve an unchaste passion.
But a man who is not moved by the love of God can still keep a precept as to the substance of the work, not from corrupt desire but from a natural affection that is not evil, and without aiming at a bad end, because he thinks it his duty and agreeable to reason. Then he commits no new sin in doing it, and the work he does has a certain moral honesty.' The good the Schoolmen call moral consists in keeping the commandments in this way, and they set it against both natural and supernatural good.
Latin
VI. Rursus observant Doctores Ecclesiae Romanae illos qui legis praecepta quoad operum substantiam observant, nec tamen istud ex charitate praestant, in duplici adhuc esse differentia. Potest enim, inquiunt, legis aliquod praeceptum servari quoad substantiam operis, etiam cum peccato, & ita ut actio laudabilis vel honesta censeri non debeat. Quum scilicet, aliquis agit ex prava cupiditate, & in malum aliquem finem, ut si quis depositum amico restituat, & largiatur aliquid egenti, sed in gratiam meretricis, & ut affectui impudico serviat. Sed quamvis aliquis Dei charitate non ducatur, potest aliquod praeceptum quoad substantiam operis servare, non ex prava cupiditate, sed ex affectu naturali non malo, & finem malum non intendens: seu quia existimat id esse sui officii, & rationi congruum: ita ut in eo novum peccatum non incurrat, sed opus quod ab eo praestatur, moralem quandam honestatem habeat. Ac in ejusmodi mandatorum legis observatione consistit illud bonum quod Scholastici morale appellant, & opponunt bono non tantum naturali, sed etiam supernaturali.