Afriend of mine, a cradle Catholic, recently discovered — and fell in love with — C. S. Lewis’ masterpiece Mere Christianity. Of course, C. S. Lewis was not a Catholic.

The question of conversion is often asked about Lewis in the light of Chesterton, whom Lewis admired. Two of Chesterton's books, The Thing and The Catholic Church and Conversion, explained his reasons for becoming Catholic. They remain marvelous books, as does Orthodoxy, a book Chesterton wrote long before he became a Catholic. One suspects that the Lord often leads us gradually, even when he can do so suddenly, as he sometimes does, as in the case of St. Paul. So perhaps Lewis was on his way when he died in his mid-60s in 1963.But we should never underestimate the importance of C. S. Lewis to Catholics. Peter Kreeft's book C. S. Lewis and the Third Millennium, is perhaps the best explanation of the abiding importance of Lewis’ thought in coming decades. In any case, Lewis and Chesterton are writers who, perhaps more than any others, explain to us why being Catholic Christians makes sense. It is not some irrational act. It is not silly. It is in fact something that is intelligible at every level, including at the level of science, which used to be the main objection to Christianity. By now scholarship has shown that many a scientific position is possible only because of some understanding of cosmic order and secondary causality that was not understood without certain Jewish or Christian teachings.

Contrary to what might be popularly assumed, but quite in conformity with the experience of anyone who has read Augustine or Aquinas, Catholicism wants to know, as Walker Percy asked, just what else is there? Aquinas is rightly famous for being able to explain fundamental objections to the faith better than could those who object to it in the first place. It is of the essence of Catholicism to know what other religions, philosophies, movements, politics, or what have you, are opposed to it or give other explanations for life purportedly superior to it. Catholicism likes Aristotle's remark that the ability to explain objections reassures us about the truth of what we uphold.

The whole ecumenical movement that John Paul II has “engineered,” together with his formal dialogues with other religions and philosophies, as far as I can tell, is based on the idea that the first step is to get a clear idea of what each variety of Christianity does hold, of what each religion or philosophy maintains about itself. Without this initial effort, no progress can be made. It is to be noticed, moreover, that today it is the Catholic Church that aggressively seeks accurately to know what other systems hold. It does not find this energy in the universities or other cultural forms seeking to know, in turn, its truth. This says rather a lot about who does and does not fear the truth.

Chesterton, in The Thing, was quite amused in his dealings with Protestant positions to find that very few of the classical reasons given for the Reformation were still held by the descendants of Christianity's breakaway sects. Many of us today, thus, find that Catholics are much closer to evangelicals and fundamentalists than we are to so-called mainline Protestant bodies. Paul Seabury once wrote a famous essay about the amazingly varied teachings of his church, the Episcopal Church, I believe, called “Trendier Than Thou.” Aside from being amusing, the phrase underscored the problem of modern Christianity, not excluding certain movements within Catholicism, of taking its cues first from the dominant culture rather than the doctrine of the faith.

We live in a time when perhaps the greatest defender of reason is not a philosopher, but, in Fides et Ratio, the Pope of Rome, who is, to be sure, himself a philosopher. Indeed, one of the great ironies of the Church today is that at its head, both in the Holy Father and in Josef Cardinal Ratzinger, we have minds superior to those constantly criticizing them in the rest of the Church and society. No doubt, there is some irony here, probably divine irony.

Aristotle warned us that we would not see the truth of things if our personal lives were disordered. The main opposition to the Church today is not from science, nor is it from intelligence. It is at bottom, I think, from a widespread unwillingness to live and believe as the Church has handed down its teachings from its founding. Whole systems, themselves gradually shown to be of doubtful validity, have been and continue to be concocted to justify the ways that seek to make of Christianity and Catholicism something other than what they are.

So, when someone raises the question of whether or not it is “OK” to become a Catholic, I confess that I think it is quite all right. It is all right intellectually. It is all right historically. It is all right in the third millennium. But it may be dangerous.

Father James Schall is a professor of government at Georgetown University.