Operating grace is distinguished from cooperating grace. Operating grace occurs when God acts on the soul without any cooperation by our free will. This type of grace is also called prevenient (from the Latin: ‘to go before’) because it occurs prior to even the possibility of an act of cooperation by our free will. Whenever we knowingly choose a holy act, an act of cooperation with grace (such as prayer or a kind deed), our act is preceded by the grace of God, acting without any possible cooperation on our part. God first touches our soul with grace, enabling us subsequently to cooperate with grace, if we freely choose to do so. This ‘first grace’ of God is before every holy act of every human person, including the Virgin Mary, and the human nature of Christ.
For example, the Virgin Mary freely chose to say ‘Yes’ to the plan of God at the Annunciation; this is called her ‘fiat’ (from the Latin: ‘let it be done’). Her fiat was a knowingly chosen holy act, done in cooperation with grace (a very full cooperation in this case). However, she would have been entirely unable to cooperate with grace at that time, and at any time, without the prevenient grace of God. Before Mary said ‘Yes’ to God, He first gave her His grace so that she would be moved and enabled to respond subsequently, in free cooperation with His grace.
This ‘first grace’ is called prevenient or operating grace, and the next grace is called subsequent or cooperating grace. Prevenient grace is called operating, rather than cooperating, because this first grace is not at all accompanied by our cooperation. At that point, the grace of God is acting (i.e. operating or working) alone. Only subsequently may we then respond to this first grace, by our free will, so as to cooperate with subsequent grace.
Prevenient grace is certainly always logically prior to subsequent grace, and it is often also chronologically prior to subsequent grace. Sometimes the sinner refuses to cooperate with prevenient grace, and so there is no subsequent grace. But the prevenient grace is given nevertheless. Even the most wicked persons on earth have frequently received prevenient grace. They are wicked not because of a lack of prevenient grace, but because they refuse to cooperate with subsequent grace. It is not the case that the wicked have turned away prevenient grace. It would be impossible to do so, because prevenient grace is first, and the refusal of grace is second. So even the worst sinners have often received prevenient grace.
Although grace is sometimes described as if God offers grace, and sinners refuse the offer, this description is not theologically accurate. When God acts in prevenient grace, it is not possible for us to refuse prevenient grace. Any response by the sinner, either refusing or accepting grace, occurs after the prevenient grace was first received. And therein lies the culpability. The sinner was truly touched by the grace of God, and subsequently the sinner refused to cooperate. The first grace of God truly affected the soul, and next the sinner refused to cooperate. All sinners have received and been affected by prevenient grace. If a refusal to cooperate with grace occurs, this refusal is always subsequent to the prevenient act of God. The human person is not able to refuse prevenient grace; he can only refuse subsequent (cooperating) grace from God. Prevenient grace always occurs without cooperation and without consent.
To use an analogy, prevenient grace is like the water in which a fish is immersed. The water surrounds him. He moves in it, and it is even within him. The fish has no choice at this point. He is immersed in the water, whether he likes it or not. The fish can then choose to swim, or not to swim in the water. But he cannot refuse to be in the water. Similarly, all human persons have prevenient grace, not merely as an offer of grace, by as an actual effect in their soul, moving and enabling them to do good. They can refuse, subsequently, to cooperate with grace, but they have already been touched by grace in this way.
This concept is absolutely essential to a proper understanding of grace. Consider what the alternative position would be. If God merely makes an offer of grace, which we must first accept before we can receive any grace, then we would have no grace with which to make that good choice to accept the offer. We would then be unable to accept any grace. For without prevenient grace, the grace that goes before, we would have no grace, and therefore no ability to accept any grace. Accepting grace from God is an act of love for God. But grace is necessary whenever the free will commits any act fulfilling the command to love God, or to love your neighbor as yourself. So this alternative position fails. The idea of prevenient grace is necessary to the concept of grace as a free gift from God. We make no choice prior to, or concurrent with, this first grace, because a previous grace would be required in order to do so. In prevenient grace, God acts alone, entirely before any act of our free will. No one ever cooperates with prevenient grace; to do so is entirely impossible. Only subsequent grace allows for cooperation.
God is morally obligated (in a manner of speaking) to give everyone prevenient grace, because He designed human nature so that it cannot function properly without grace and cannot avoid sin without grace. God cannot deny prevenient grace to any human person, not even to the worst of sinners, for He cannot act contrary to His own plan for human nature. Therefore, prevenient grace is not merely offered to all sinners; prevenient grace affects all sinners. Prevenient grace never fails to affect each and every soul, even those that are very sinful, even if they are in a state of actual mortal sin. It is the refusal to consent to, and cooperate with, subsequent grace that distinguishes the sinful person from the holy person. Prevenient grace occurs without consent or cooperation; subsequent grace requires consent and cooperation.
The above text is an excerpt from my book:
The Catechism of Catholic Ethics: A work of Roman Catholic moral theology, from chapter 30: ‘Grace and Salvation’.