Yesterday I excerpted Machen on the uniqueness of the Bible. It's "a revelation which sets forth the meaning of an act of God." He goes on to address some objections to that view, and also discusses how personal experience can/does validate the effectiveness of something that happened long ago, namely, the death and resurrection of Jesus. In other words, take Jesus up on his claims and see if he doesn't become to you more than a mere historical figure, but the living Saviour of today. However, he's quick to point out that divorcing experience from the historical nature of the gospel leads to all kinds of errors.
But not only do Christians believe that the Bible is unique, we believe it is true, even inspired. What does it mean to say the Bible is inspired? Machen sets out the classical Protestant view of the Bible as the "infallible rule of faith and practice" and offers a defense of the doctrine of plenary inspiration. On the latter point he's not as dogmatic as elsewhere in the book, since there have been many Christians throughout history who've had differing views on the nature of Biblical inspiration. If you want to read more about this subject, here is a good place to start. Once again, from Christianity and Liberalism, J. Gresham Machen on the inspiration of the Bible:
The contents of the Bible, then, are unique. But another fact about the Bible is also important. The Bible might contain an account of a true revelation from God, and yet the account be full of error. Before the full authority of the Bible can be established, therefore, it is necessary to add to the Christian doctrine of revelation the Christian doctrine of inspiration. The latter doctrine means that the Bible not only is an account of important things, but that the account itself is true, the writers having been so preserved from error, despite a full maintenance of their habits of thought and expression, that the resulting Book is the "infallible rule of faith and practice."
This doctrine of "plenary inspiration" has been made the subject of persistent misrepresentation. Its opponents speak of it as though it involved a mechanical theory of the activity of the Holy Spirit. The Spirit, it is said, is represented in this doctrine as dictating the Bible to writers who were really little more than stenographers. But of course all such caricatures are without basis in fact, and it is rather surprising that intelligent men should be so blinded by prejudice about this matter as not even to examine for themselves the perfectly accessible treatises in which the doctrine of plenary inspiration is set forth. It is usually considered good practice to examine a thing for one's self before echoing the vulgar ridicule of it. But in connection with the Bible, such scholarly restraints are somehow regarded as out of place. It is so much easier to content one's self with a few opprobrious adjectives such as "mechanical," or the like. Why engage in serious criticism when the people prefer ridicule? Why attack a real opponent when it is easier to knock down a man of straw?
As a matter of fact, the doctrine of plenary inspiration does not deny the individuality of the Biblical writers, it does not ignore their use of ordinary means for acquiring information; it does not involve any lack of interest in the historical situations which gave rise to the Biblical books. What it does deny is the presence of error in the Bible. It supposes that the Holy Spirit so informed the minds of the Biblical writers that they were kept from falling into errors that mar all other books. The Bible might contain an account of a genuine revelation of God, and yet not contain a true account. But according to the doctrine of inspiration, the account is as a matter of fact a true account; the Bible is an "infallible rule of faith and practice."
Certainly that is a stupendous claim, and it is no wonder that it has been attacked.
J. Gresham Machen, Christianity and Liberalism, pp. 72-74