Jerry L. Walls is not a Catholic. He is professor of philosophy and religion at Asbury Theological Seminary, a conservative evangelical Methodist seminary in Wilmore, Kentucky. He teaches an annual C.S. Lewis seminar, which is one of the school's most popular offerings. Thirteen years ago he published a widely-discussed book entitled Hell: The Logic of Damnation (Notre Dame, IN: University of Notre Dame Press, 1992). Ten years later, he has published Heaven: The Logic of Eternal Joy (Oxford: Oxford University Press, 2002), which has also been receiving wide attention, among other things for his treatment of Purgatory.
To his credit, Walls is willing to take Catholic teaching seriously. In particular, in his new book he defends the doctrine of Purgatory as an essential concomitant of the doctrine of Heaven. The basic idea of Heaven is embodied in the classic notion of the beatific vision, which involves the saved believer's everlasting life in God's presence. The problem, of course, is that it's hardly possible to conceive of anyone who could possibly be worthy of dwelling in God's presence, or even desirous of doing so, who has not attained complete sanctification, complete holiness--the final moral purification for which the typical believer, despite his best efforts, achieves only an imperfect approximation in this life. Since even the most devout Christian typically has not attained that goal at death, the only remedy can be an intermediate period between death and the beatific vision during which the believer's preparation is completed. This, of course, would be what Catholic tradition means by Purgatory.