Cap. VIII Arg. 4 Resp.: negative reprobation not for damning; Cajetan; riches of mercy (Rom. 9:23)
If we speak of that negative reprobation by which God firmly decreed of some particular person — say Cain or Judas — not so far to have mercy as to will to draw him efficaciously out of sin and misery, and at the same time decreed to permit his final hardening in sin: I deny God does this to fulfill a purpose of vengeance or damnation. Cajetan puts it well on Aquinas I, q. 23 a. 5: God does not permit sins in order to punish, but permits and punishes for the shining forth of his justice. Paul himself in the cited place shows that God denies this special mercy to some, thereby permitting them to be hardened — wherein negative reprobation consists — not with primary intent to damn those thus passed by, but to manifest the riches of his mercy toward the elect (Rom. 9:23). Only then do the elect see they were saved by pure mere mercy: when it is plain that the calling according to purpose granted them by gratuitous good pleasure was denied to others; that they were no better than those passed by as to corrupt nature, in which special mercy found them; and that they would have been no less hardened than the reprobate unless mere divine favor had softened them by that special grace.
Latin
Si de negativa illa reprobatione sermo habeatur qua Deus firmiter decrevit singularis alicujus personae, puta Caini aut Judae, non eatenus misereri, ut velit illum efficaciter e statu peccati et miseriae eruere, ac simul decrevit permittere ejusdem in peccatis suis finalem indurationem; nego hoc fieri a Deo ob eum finem ut vindicandi sive damnandi propositum expleat. Non male hac de re philosophatur Cajetanus in Commentariis suis ad 1am Aquinatis, qu. 23. art. 5, ubi dicit, Deum non permittere peccata ut puniat, sed permittere et punire propter relucentiam justitiae suae. Quinetiam ipse Apostolus loco citato indicavit nobis, Deum specialem hanc misericordiam aliquibus negare, atque inde permittere ut indurentur (qua in re consistit negativa reprobatio) non intentione primaria damnandi hosce sic praeteritos, sed Manifestandi divitias misericordiae suae erga ipsos electos, Rom. ix. 23. Nam tum demum intelligunt electi se fuisse pura et mera Dei misericordia salvatos, cum constet denegatam fuisse aliis illam vocationem secundum propositum quae ipsis ex gratuito Dei beneplacito fuit concessa; cum constet illos nihilo fuisse meliores hisce praeteritis quoad conditionem naturae corruptae, in qua specialis misericordia eos deprehendit; denique cum constet eos futuros fuisse non minus induratos ipsis reprobis, nisi ex mero Dei favore hac speciali gratia fuissent emolliti.