The Dutch-American Calvinist raised in the Midwest and now the John A. O'Brien Professor of Philosophy at the University of Notre Dame is not just the best Christian philosopher of his time. No, Plantinga is the most important philosopher of any stripe.
Plantinga deserves this accolade for three reasons.
First, he has taken up the two most important questions of our day: the problem of evil (arguably the most important philosophical question of any era) and the problem of knowledge (undoubtedly the key philosophical question of our era).
Second, he has made fundamental contributions to these two questions. On the problem of evil, Plantinga's vaunted "Free Will Defense" (to which we'll return in a moment) responded to the most trenchant form of this problem with a success rarely found in philosophy: for almost 20 years now, the discussion of the problem has shifted to other grounds because of the widespread acknowledgment of Plantinga's argument. In the case of epistemology (the theory of knowledge), his proposal is so recent that we must wait to see how it will fare. Indeed, the third volume of his epistemological trilogy on "warrant" was published only last year (Warranted Christian Belief, Oxford University Press). So far, however, it seems to have met all of its contemporary challenges.
Third, Plantinga has dealt with these two crucial issues on behalf of orthodox Christian faith. Because of the excellence of his labors, the Christian view of things simply has to be taken seriously by any questioner with the integrity to appreciate sound philosophy. Plantinga's greatness, then, lies also in his working on behalf of the truth—an admittedly biased judgment ...