The difference between a Calvinist and a Thomist is that the former go around calling themselves the predestinate. Thomists live as to make their calling and election sure. We believe that God’s grace is all in all, but God’s grace also enables man to act. There is a response. God initiates it, of course. He also gives us the grace to respond and persevere.
The problem is, that unless someone is both a thomist and a universalist, God simply omits some people from the possibility of salvation, which is not compatible with his universal salvific will, which is not salvific merely in a figurative, antecedent way. It is a truly and genuine salvific will.
Again, Pope Saint John Paul II has been very clear about this point
Pope John Paul II: “The universality of salvation means that it is granted not only to those who explicitly believe in Christ and have entered the Church. Since SALVATION IS OFFERED TO ALL, IT MUST BE MADE CONCRETELY AVAILABLE TO ALL. But it is clear that today, as in the past, many people do not have an opportunity to come to know or accept the gospel revelation or to enter the Church. The social and cultural conditions in which they live do not permit this, and frequently they have been brought up in other religious traditions. For such people salvation in Christ is accessible by virtue of a grace which, while having a mysterious relationship to the Church, does not make them formally part of the Church but enlightens them in a way which is accommodated to their spiritual and material situation. This grace comes from Christ; it is the result of his Sacrifice and is communicated by the Holy Spirit. It enables each person to attain salvation through his or her free cooperation.” (Redemptoris Missio, n. 10).
In the classical thomist system, with both intrinsically efficacious Grace, sufficient Grace as understood by the thomists AND unconditional negative Reprobation on top of that, salvation is simply not concretely available to all. It is only potentially available to all, but the reprobate has no chance, no ACTUAL chance, to avoid the sin of final impenitence.