I offer this dramatic introduction only half-seriously, which means I'm only half-joking.
By reading some of Van Til's followers, you would think he authored the first thoroughly biblical understanding of the knowledge of God. That might be saying too much, but it is indeed difficult to find someone with more penetrating insight about the failures of natural man's understanding of God, himself, and the world. His thinking in apologetics and epistemology would soon come to be known as presuppositionalism---a term Van Til disliked and others have tried to remedy.
Van Til transformed the discussions around epistemology and apologetics unlike anyone else in modern Christian history---being the main influence behind theologians, pastors, and apologists like John Frame, Tim Keller, David Powlison, Greg Bahnsen and the entire systematic and apologetics departments of Westminster Theological Seminary in Philadelphia and California, headed by names like Michael Horton, Scott Oliphint, William Edgar, and David VanDrunen. Yet it's not likely that most Christians---even thoughtful ones---could recognize his name, much less name a book he's written.
English as a Second Language
Van Til's obscurity has a lot to do with his dense books. As John Muether observes in biography of Van Til, English was his second language, putting him at a handicap in clarity and prose. His critics sometimes don't even bother to read Van Til for themselves, choosing to disparage him through secondary sources.
John Frame wrote in The Doctrine of the Knowledge of God in 1987, "Cornelius Van Til's apologetic has taken some giant steps toward reforming our Christian epistemology and theological method." Yet despite these "giant steps forward," Van Til's developments "have not profoundly affected the contemporary teaching of systematic theology or the preaching and popular theologizing of our day."
Still, there are signs that his influence has spread in recent decades. David Powlison writes about Van Til's influence on the biblical counseling movement: "I would say that if you were to look at primary sources for what biblical counseling is, that Scripture, orthodox theology are gonna be what you'd first say. But from a deep structure standpoint, it is Van Tillian utterly from beginning to end."
The pastoral payoff of reading Van Til, I have found, is that he shows why a lack of knowledge about God is more about a lack of love for God. This connection helps pastors trying to show the compelling nature of the gospel but also the desperate need of the human heart. Van Til provides the resources for pastors to legitimately say to skeptics, "Deep down inside, you know something is profoundly wrong, and you are holding it down in unrighteousness."
Where to Begin?
The difficulty of picking up a new author, especially someone who is as challenging as Van Til, is figuring out where to begin. I asked three apologists influenced by Van Til where someone might begin reading:
Michael Horton, professor of apologetics and theology at Westminster Seminary California, Escondido, California:
Defense of the Faith, edited by K. Scott Oliphint (P&R, 2008). Make sure you have this edition, since the editor's notes are helpful in explaining the context of many of Van Til's references and interlocutors.
Eric Sigward, ed., The Works of Cornelius Van Til, 1895-1987, CD-ROM. This collection of Van Til's work in one place, along with digital photos and audio recordings, is a great reference.
There are also good secondary works on Van Til's thought:
Greg Bahnsen, Van Til's Apologetic: Readings and Analysis (P&R). Bahnsen both explores and also extends Van Til's thinking in the light of more recent debates.
John Frame, Apologetics to the Glory of God: An Introduction (P&R). A readable apologetic from Van Til's perspective.
Thom Notaro, Van Til and the Use of Evidences (P&R). This little book is especially helpful for explaining the positive use of evidences in Christian apologetics.
K. Scott Oliphint, professor of apologetics and theology at Westminster Theological Seminary in Philadelphia:
The Defense of the Faith, fourth edition (P&R). This book is really the culmination of the approach Van Til had been developing for decades. First published in the mid-1950s, Van Til wrote it to (1) present his approach as one that is consistent with and entailed by Reformed theology (so he begins the book with that theology) and (2) to address some of the criticisms that he had previously encountered. The fourth edition is the complete first edition, but with my editorial footnotes and comments. Thus, it is the only "complete" edition in that it includes material not included in any of the other, subsequent editions that were printed.
Common Grace and the Gospel (P&R). This collection of essays shows both what common grace is, from Van Til's perspective, and how it applies to his apologetic approach. This book may be the most important, and most misunderstood (or neglected) book that he wrote. It is particularly appropriate now that there seem to be views of common grace that, contra Van Til, see it as a "realm" or "territory" in which God's reign is either neutralized or severely restricted. Once Van Til's method is grasped (as presented in The Defense of the Faith), the principles of common grace, which themselves presuppose the covenantal antithesis, must be understood as essential to a proper understanding and application of that apologetic method.
A Survey of Christian Epistemology (or found in The Works of Cornelius Van Til, CD-ROM). This "syllabus" is a revision of the first syllabus Van Til published. Originally entitled The Metaphysics of Apologetics, the principles he works through in this book show the necessity of being, as he says in numerous places, "epistemologically self-conscious." Though this work is dated in terms of some of the issues and problems he addresses, the principles he applies to those issues and problems show clearly the necessity of his epistemological starting point, which is, of course, revelation. This book is difficult, but once its main argument is grasped, everything else in theology will begin to take on a different, more foundationally biblical, cast.
John Frame, professor of systematic theology and philosophy at Reformed Theological Seminary in Orlando:
Christian Apologetics. This is the book he used as an introductory text to his first-year students.
"Why I Believe in God," pamphlet. Fascinating piece.
The Defense of Christianity and My Credo (found in The Works of Cornelius Van Til, CD-ROM), summarizes his apologetic.