For many, the mercy of God seems incompatible with the doctrine of hell. If God is all-merciful, then wouldn’t he have mercy on the damned and give them the grace they need to repent? Although the damned wouldn’t be able to reorient their wills to God naturally, given the irrevocability of the will after death, perhaps God could give such a grace that would enable them to change their wills supernaturally. Since God doesn’t give this grace, then he isn’t all-merciful.
Even if we assume for argument’s sake that God could give a grace of repentance to the damned despite the natural irrevocability of the will after death, the major problem with the objection is that it assumes that God must give the grace of repentance to be merciful. But this assumption is false. And the reason it’s false is that it entails a contradiction.
Mercy, by definition, is an act of giving that which a person doesn’t have to give. For example, if you have a debt and owe me money, I could easily require in justice that you pay the debt. But I could also just as easily exercise mercy and remit the debt. The reason it would be an act of mercy is that I didn’t have to remit the debt, yet I did, gratuitously.
So to say that God must give the grace of repentance to be merciful—whether to the damned or us in this life—is to say that giving the grace of repentance is an act of mercy and not an act of mercy at the same time and in the same respect. It would be an act of mercy simply by virtue of saying that God is merciful. And it would not be an act of mercy insofar as the objection assumes that God must give the grace. That’s a contradiction.
Since the fundamental assumption of the objection—namely, that God must give the grace of repentance to be merciful—entails a contradiction, we can conclude that the objection from God’s mercy has no persuasive force against affirming the reality of hell.