That God is merciful signifies that God gives to His creatures benefits that go beyond the requirements of justice. If we assume, as Thomas does, that existence itself is a good, then God’s mercy is in evidence in His creating us, since none of us had (prior to existing) a right to exist based on some merit of our own. However, natural reason (as exercised in natural theology) cannot inform us about the degree or extent of God’s mercy.
Since the universe if finite and necessarily imperfect, God’s mercy toward us is also necessarily finite, despite God’s own infinite goodness. God must set some finite limit to His mercy and love, and this limit must necessarily be arbitrary, since mercy by definition goes beyond the requirements of justice. It is incoherent to expect infinite love from God, since this would require him to make each of us into duplicate of Himself, which is metaphysically impossible.[1] Just as the infinite power of God implies that there is no best possible world, it also implies that there is no best possible life for each of us. [2] Consequently, we must look to sacred theology, to what God has revealed to us in history, the Scriptures, and Tradition, in order to learn exactly what form God’s mercy takes.
It has been popular for some time now to say that God’s love is unconditional. This is true in one sense, and false in another. The love that God displays in creating us is unconditional, since it was impossible for us to satisfy any condition before we existed. However, it does not follow that we all benefit unconditionally from God’s love, or that we benefit equally from it. It is not surprising that God sets conditions on our receiving benefits from His love—for example, the condition of our freely cooperating with the supernatural gifts that He offers us. We must choose to avail ourselves of the means that God has provided for our growth and maturation, including the Gospel and the sacraments of the Church. We cannot reasonably complain to God if we have been negligent in taking advantage of those means. God’s love for us does not ensure that all of us will do so. The reason so many, both theists and atheists, struggle with the problem of evil is that they start with the assumption that God’s love for each of us is infinite and unconditional. But sober reflection reveals that assumption to be groundless.
It is puzzling that so many people who know or at least suspect that God exists do little or nothing to be reconciled with God. There are two possible explanations: complacency and despair. Some may think, erroneously, that God’s benevolence toward them is infinite and unconditional, and so they can be confident of enjoying the best possible existence, no matter what they do. Others suppose, also wrongly, that they have been so immoral in the past that there is no chance of winning God’s favor. The first error is philosophical in nature, and the second more theological. God’s love is conditional, but the condition can be satisfied by all, no matter what they have done:
“Say to them, As I live, says the Lord God, I have no pleasure in the death of the wicked, but that the wicked turn from his way and live; turn back, turn back from your evil ways; for why will you die, O house of Israel?” (Ezekiel 33:11, RSV)
“Just so, I tell you, there will be more joy in heaven over one sinner who repents than over ninety-nine righteous persons who need no repentance.” (Luke 15:7, RSV)
[1] In the Nicomachean Ethics, Book VIII, chapter 7, Aristotle notes that no one would wish the greatest possible good for his friends, since enjoying the greatest good would be to become a god, but this would be incompatible with the friend remaining himself. For the same reason, God can only wish us to enjoy some finite level of value.
[2] Peter teaches that believers will be “partakers of the divine nature” in the next life. (2 Peter 1:4, RSV) Isn’t that the best possible state we could enjoy? It’s true that it is a state that is relatively infinite, compared to the goods available in this life, in the sense that it is immeasurably better than any such good. But to “partake” of God’s nature is not to become another God. And our enjoyment of our union with God is always bounded or finite, and so always improvable (see Summa Theologiae I, Q12, a6 and I, Q25, a6). Therefore, nothing God could give us would be absolutely infinite.
The Analytic Thomist 