This chapter of How to Know God Exists is different. Ray argues for the first half of the chapter that on the one hand the Bible is clearly of supernatural origin, and hence further proof of God, and in the second that the Bible is not actually necessary in order to know God and be saved. Note that this is not a contradiction or absurdity: the earliest church did not have the New Testament and were not unanimous on what constituted the Old Testament (and many were illiterate and could not read such scriptures as they had). But it does result in a rather sharp change in tone and method halfway through the chapter.
Ray offers two main lines of evidence for the supernatural inspiration of the scriptural text, knowledge of creation (nature) and knowledge of the future. "Over 25 percent of the Bible contains specific predictive prophecies that have been literally fulfilled" Ray states, and "only One Who is omniscient can accurately predict events thousands of years in the future." There are three problems with this position.
First, just to nitpick, as anyone who's ever read a time-travel story should realize, the ability to predict some things about the future doesn't necessarily include the ability to know everything about the future, past, and present. Even in the Old Testament, God's ability to foretell the future is often presented as indistinguishable from His power to bring about the events He foretells: not omniscience, but simply sufficient power to overcome any opposition. If you're arguing literally for God -- not merely a being much more powerful and capable than we mere humans are, but an omnipotent, omniscient Ruler and Creator -- prophecy may not good enough because it's not hard enough.
Second, though, is not a nitpick: some of the actual examples Ray provides of fulfilled prophecy depend on the assumption that that Bible provides an inerrant account of the life of Jesus. We know that the gospels say that Jesus was born of a virgin in Bethlehem, was betrayed for 30 pieces of silver and buried in a rich man's tomb. We don't actually know that the Bible is right on any of these points. Conversely, we're pretty sure that Alexander the Great's conquest of Persia happened and is referred to (in symbols) in the book of Daniel, but we have no evidence that Daniel was written before rather than after that conquest. We have to assume that the Bible is accurate to accept the evidence that Ray offers for the accuracy of the Bible.
Third, Ray is stretching a point when he speaks of "specific predictive prophecies" that are "literally fulfilled." He notes, as one striking prophecy almost certainly issued before archaeologists and historians tell us it was fulfilled, Ezekiel's prophecy of the destruction of Tyre. Ezekiel predicts that this will be accomplished by Nebuchadnezzer, probably after Nebuchadnezzer had already started his campaign against Tyre. Ezekiel doesn't mention Tyre holding out in is offshore redoubt for another two or three centuries until Alexander the Great shows up. He does predict that the city will be totally destroyed, which is hard to reconcile with the fact that it still existed in Jesus' day (it is referred to in the New Testament), and indeed there is still a village by that name (Arabic Sur, cognate with Canaanite Sor) there today. The prophecy is literally and exactly fulfilled, for a loose and non-literal sense of "literally and exactly."
The same point applies, indeed, to many of the prophecies said to be fulfilled by Jesus. Isaiah's "virgin birth" prophecy may not predict that the child will be born to a literal virgin, and in any case refers to a sign offered to King Ahaz of Judah seven centuries before the birth of Jesus. The prophecy in Zechariah that speaks of giving thirty pieces of silver to the potter is in connection with a threat to withdraw God's protection from a disobedient Judah; there is nothing in the text to suggest that it is Messianic. We need to accept the New Testament writers' interpretation of the verse, as well as their claim that Judas betrayed Jesus for this price, to see it as a fulfilled prophecy. Daniel definitely predicts (or refers back to) Alexander the Great, but his supposed references to the Roman Empire might as easily, or more easily, refer to the regime of Antiochus Epiphanes (to whose career so much of the book refers, and whose overthrow is implied in Daniel to usher in the Messianic Empire).
Ray argues that even one fulfilled prophecy would prove the Bible's supernatural origins. Given his insistence on the Biblical standard for prophecy (100% accuracy), one wonders if he would concede the converse: if Nebuchadnezzer didn't render Egypt an uninhabited wasteland for thirty years, does this prove that the Bible contains uninspired, purely natural works?
But a more direct objection is that on Ray's own showing, prophecy is sufficiently open to interpretation and reinterpretation that some passage can be re-made into a vaticinium ex eventu, a prediction after the fact, for almost any event. One can see this in the last century: it was said, a century ago, that it was sufficient proof of divine inspiration to read Barnes' Notes on Revelation side by side with Gibbon's Decline and Fall of the Roman Empire. The startling correlations Barnes noted between the text of Revelation and, e.g. the Turkish invasions of the Eastern Roman Empire still exist, but the fashion for interpreting Revelation has changed, and now we are to marvel, instead, at the striking correlations between Revelation and the existence of bar code readers, the European Union, and the establishment of modern Israel.