Cap. 1 prol. IV: Fathers treat such conditions as meritorious causes — Aug. Ep. 105
I dare say Augustine and the other Fathers treat it this way: whenever some human quality or act is so required beforehand that when it is present some following gift of God is present with it, and when it is absent that gift is denied, they set that quality or act in the place of a cause — a cause, as they put it, meritorious in its own way. A condition demanded by God's ordination and performed by the person through God's grace has, for the Fathers, the force and nature of a meritorious motive cause with respect to the benefit conferred under that condition. So Augustine in Epistle 105: the very remission of sins is not without some merit, if faith obtains it. By the same reason, election to glory will not be without some merit on the elect person's side, if faith obtains it. For among the Fathers merit is nothing but a work which, by God's ordination, obtains some benefit. So if the benefit of election is conferred on us from our foresight act of believing, that is not a mere condition sine qua non — it is a cause, indeed the merit of the following benefit, in the sense in which the Fathers use the word merit.
Latin
Ausim affirmare Augustinum reliquosque Patres, quandocunque qualitas aut actio aliqua humana ita praerequiritur, ut illa posita ponatur simul consequens aliquod Dei beneficium, illa absente negetur, habere talem qualitatem aut actum causae loco, causae (ut illi loquuntur) suo modo meritoriae. Conditio enim secundum ordinationem Dei postulata, & per gratiam Dei ab homine praestita, habet apud Patres vim & naturam causae meritoriae motivae, quoad beneficium sub tali conditione conferendum. Sic loquitur Augustinus Epist. 105. ubi dicit, ipsam remissionem peccatorum non esse sine aliquo merito, si fides hanc impetrat. Pari ratione electio ad gloriam non erit sine aliquo merito ex parte electi, si fides illam impetrat. Nam meritum apud Patres nihil aliud est, quam opus ex Dei ordinatione alicujus beneficii impetratorium. Si ergo ex praeviso nostro actu credendi conferatur in nos beneficium electionis, non est conditio sine qua non, sed est causa, imo meritum sequentis beneficii, eo sensu quo Patres usurpant hoc meriti vocabulum.