Grace only perfects and helps nature
Thesis XCIX. Molina gives grace no other role than to perfect nature and help it in its own motions, so that each person becomes, through supernatural aid and grace, what salvation requires. To identify and explain the motions of grace, therefore, he wants us to look at the course and order that nature itself, or the knowing and desiring powers, would follow if they produced, by their own strength alone, the substance of the same acts that are attributed to grace. He thinks this can happen.
In this way we are to understand how God, through the aids and gifts of grace, inserts himself into nature, cooperates with it and helps it, so that it produces beyond its own strength such acts as are necessary for salvation.
Latin
XCIX. Jam autem Doctor ille non aliud gratiae tribuit quam ut perficiat naturam, eamque adjuvet in suis motibus, ut unusquisque ex supernaturali auxilio & gratia talis sit, qualis ad salutem oportet. Ac proinde ad dignoscendos & explicandos motus gratiae, vult attendi ad progressum & ordinem, quem natura ipsa, potentiaeve cognoscentes & appetentes servarent, si illos eosdem actus, qui gratiae tribuuntur, suis solis viribus quoad substantiam actus producerent, quod fieri posse ille existimat. Ut ea ratione intelligatur quo pacto Deus per auxilia ac dona gratiae, se inserat & cooperetur cum natura, eamque adjuvet, ut supra suas vires eos actus producat quales ad salutem necessarii sunt.