The following argument is valid:
- (Premise) No life lived virtuously can have been wasted.
- (Premise) If God doesn't exist, a life lived virtuously can have been wasted.
- Therefore, God exists.
But of course the question is whether the argument is any good, at all useful towards giving someone reason to accept the conclusion. Well, I do find myself with a certain pull towards (1) and (2) independently of theism. Claim (1) just seems right to me. But if God doesn't exist, then it does seem quite possible for someone's central life pursuits to have been unsuccessful, despite these central life pursuits being virtuous.
However, I have the following worry. Maybe no life lived virtuously can have been wasted, because what it is to have wasted a life is to have failed at one's central pursuits or to have centrally pursued only vanities. But a virtuous person always has her own virtue as a central pursuit, and hence a virtuous person's life is never wasted, as one of her central non-vain pursuits—that of her own virtue—has been successful. Thus, even if God doesn't exist, a life lived virtuously couldn't have been wasted.
But I think that if theism were false, then a virtuous person might never centrally pursue her own virtue. For it could be that she is faced with needs more urgent than the pursuit of her own virtue—feeding a starving family, say—and so virtue could require her not to centrally pursue her own virtue. And if this is rigth, then (2) is non-trivially true. If God did not exist, there would be a possibility of a wasted virtuous life. It would be a life where one has virtue but does not pursue it as a central part of one's life, because virtue itself prohibits making the pursuit of virtue central.
If Christian theism is true, however, other duties will not be sufficient to shift the pursuit of virtue into something of secondary importance. For the Christian can have a trust in Providence that we will not go wrong by making our pursuit of union with God (which requires the pursuit of virtue) central to our lives.
This gives a second version of the argument:
- (Premise) If theism is false, then a virtuous human being can be in circumstances such that she should assign only secondary importance to the pursuit of virtue.
- (Premise) It is not possible for a human being to be in circumstances in which she should assign only secondary importance to the pursuit of virtue.
- Therefore, theism is true.
I do not find the two arguments in this post deeply compelling. But I think they at least should somewhat raise the probability of theism for those for whom it is neither zero nor one.