At the heart of the debate on grace is the detailed process of how conversion occurs.
We know that as far as Ephesians 2:8-9 tells us, grace is an integral part of our conversion. It is by grace that we are saved, nothing more and nothing less. On that account, everyone is clear. Both Calvinism and Arminianism will agree that grace is required and must precede man’s conversion. What they differ in is with their views of how much grace compels and changes man.
For Calvinism, the conversion of man is by virtue of Irresistible Grace. Remember that the starting condition of man is one of Total Depravity. This means that man cannot and will not choose God. In fact, Total Depravity necessitates that man will do everything that he can to actually resist God. Therefore, in order for man to be saved, a force greater than his resistance must be applied to overcome it. That is why when God dispenses saving grace to man, it must be irresistible. For if it was resistible, then the totally depraved man will resist this.
However, since grace is irresistible, it must necessitate that only the elect will experience this grace. Therefore it is important to make a distinction between an external call to salvation (hearing the Gospel) and an internal call to salvation (the Holy Spirit regenerating man). The external call is resistible. The internal one is not.
So in this view, God’s execution of his election is done by first applying his saving grace to man, thereby regenerating him prior to faith. Faith is only possible because of the full regeneration that God did on man. Thus the series of events are total depravity, then grace, then justification and regeneration, then faith, then sanctification.
We see this concept in verses like Romans 8:30, where Paul carries a certain sense of definiteness that those whom God called he will also definitely justify. Likewise Jesus himself taught in John 6:37-39 that all whom the Father gives him will definitely come to him and in John 6:44-45 that it is the Father who draws them. The sense of definiteness in these verses suggest that the drawing that God does appears to be absolutely effective. Moreover, Ephesians 2:5 also tells us that God made us alive with Christ when we were dead in transgression. Being dead in transgression, it is impossible for man to have faith, and thus the regeneration must precede faith.
Hence, in Calvinism, conversion is monergistic, meaning it is solely the work of God. It is operative in that it is directly applied by God to man without any need for man’s cooperation.
An important thing to note, though, in the idea of Irresistible Grace is that it is not a violent imposition that the Holy Spirit bring onto man. Rather it is a transformative one.
On the other hand, Arminianism teaches the doctrine of Prevenient Grace. Prevenient is just a term that basically means that it precedes something. Grace still is t he starting point of conversion, however it is strictly speaking just the preparatory work of the Holy Spirit, and not the full story of conversion. The idea is that when God dispenses saving grace to man, what it does is it merely a partial regeneration of human will. Man, after receiving God’s grace, is not fully regenerated, but only partially to the point where it is now possible for man to respond in faith. Prevenient Grace is then the grace by which God creates the possibility for man to have faith, and not just a possibility, but a strong influence towards faith. However, this grace is still ultimately resistible.
The concept of Prevenient Grace is important to the doctrines of Conditional Election and Unlimited Atonement, and vice versa. Since salvation is a possibility for all but will not be availed by all, then Prevenient Grace must be applied to all but at the same time be resistible.
So in this view, God’s invitation to salvation is done by partially regenerating man’s will by grace so that he can respond in faith. Faith is only possible because of the partial regeneration that God did on man, and this particular faith will then trigger the full regeneration of man. Thus the series of events are total depravity, then grace, then partial regeneration, then faith, then justification and full regeneration, then sanctification.
We see this concept in verses like John 12:32, where Jesus mentions that he will draw all men to himself. Likewise, Revelations 22:17 extends the offer of salvation to anyone.
Hence, in Arminianism, conversion is synergistic, meaning that multiple parties are involved. The cooperation of man in responding is a necessary part of conversion.
An interesting thing to note with the idea of Prevenient Grace is where human responsibility comes in. Because grace is resistible, then a significant focus is given to the fact that man must be held accountable if he so finally decides to resist this grace that has been given to all. But exactly how or when this grace is given to each individual is unclear and might differ from person to person.
Regardless, both agree that God’s grace is the first step in our salvation and that because of this, we are saved by grace. What they disagree is whether this is the sole step or not.