The message of this famous classic of the Christian faith is more desperately needed in the 21st century than it was in the early 20th century. Since Machen wrote, the philosophical and theological trends that generated the issues he was addressing have become more firmly entrenched in the consciousness not only of the culture at large, but of evangelical Christianity in particular. The major thesis of this books is not that theological liberalism is bad, although Machen leaves little doubt of his opinion of it. Rather, the major thesis is that theologically liberal Christianity is not Christianity at all, and that toward every one of the most fundamental teachings of historic Christianity, theological liberalism takes an antithetical stance. These fundamental teachings are expounded in seven brief chapters, covering an introduction, doctrine in general, God & man, the Bible, the person of Jesus Christ, salvation, and the church.
The position of the liberal church toward doctrine is that Christianity should be an undogmatic religion, unconcerned with theological subtleties. Christianity should be a life, not a system of doctrine. Certainly at this point, liberalism could not possibly be more firmly allied with contemporary mainstream evangelicalism. Anti-doctrinalism goes hand in hand with the two most pervasive philosophical currents of our age, postmodernism with its radical relativism, and existentialism, with its radical subjectivism and distrust of objective systems in general. Machen shows that the religion of both the apostle Paul and Jesus Christ himself was as dogmatic as possible. For example, even in the Sermon on the Mount, a favorite passage among theological liberals, "Jesus represents Himself as seated on the judgment seat of all the earth . . . Could anything be further removed than such a Jesus from the humble teacher of righteousness appealed to by modern liberalism?"
Concerning God and Man, Machen emphasizes the liberal tendency to break down the separateness between God and Man and to take an optimistic view of human goodness. One of the most penetrating insights in the book is that "modern liberalism, even when it is not consistently pantheistic, is at any rate pantheizing." This is in opposition to the orthodox teaching of the absoluteness of the Creator-creature distinction, and also of the absolute moral gulf between God and Man as a result of sin, hopelessly unbridgeable apart from the work of Jesus Christ.
Related to the aversion of liberalism to doctrine, or an objective summary of truth, is a corresponding mistrust of the Bible, and the rejection of the Bible's authority as God's Word. Liberalism claims to replace the authority of the Bible with the authority of Jesus Himself, but having rejected the teachings of Jesus in the Bible and through the apostles, this authority amounts to nothing more than the authority of personally selected isolated instances of Jesus' words, interpreted to conform to the liberal religion.
In the person of Jesus Christ, liberalism sees an example for faith, but not an object of faith. This is because the driving principle of liberalism, anti-supernaturalism, cannot admit the historical teaching of who Jesus Christ really was. For liberalism "Jesus differs from the rest of men only in degree, and not in kind: He can be divine only if all men are divine."
Concerning salvation, liberalism sees the source of salvation in man; Christianity sees it in God. Machen also shows that what distinguished early Christianity from the pagan religions of the time was specifically its exclusiveness. Paganism, like modern liberalism, had no problem with many roads to God and many gods, but it has a very deep problem with the exclusivity of Christianity. Finally, the very concept of salvation in Christianity is concerned with heaven, or the future world and life, while modern liberalism is concerned only with this world. This is in my estimation the area in which the majority of Reformed Christians have in fact followed liberalism, specifically with the contemporary preoccupation with cultural transformation as the means to institute God's kingdom on this earth. This is precisely the idea that unambiguously characterizes unbelieving thought, from the rebellious nation of Israel, through the Pharisees, and into the Enlightenment and modern liberalism. Until the European Enlightenment, the true church had consistently affirmed that the world is not our home.
The final chapter on the church is where we have the best glimpse of Machen himself. What Machen could not understand was that if liberalism was so clearly another religion, why it insisted on calling itself Christianity. As far as he was concerned, this was just plain dishonesty. It is in this chapter that he says that he has no problem with liberalism establishing itself as a separate religion competing with Christianity. But calling itself Christianity when it was clearly not, spreading its non-Christian teachings to Christians, and with liberal ministers taking ordination vows to historic confessions of faith which could not possibly be sincere, this was the liberalism against which Machen fought for his whole life, a battle which in the mainline Presbyterian church he ultimately lost. This book clearly and powerfully sets forth what was at stake in the battle, which was and remains nothing other than Christianity itself. The book is well worth reading for all Christians who are committed to their faith. It is not a difficult book to read, and the fundamental issues have changed very little in one hundred years.