"What if someone claims to have read the Bible and says it’s just a book of fairy tales?"

Call his bluff. Gently ask, "What is the thread of continuity that runs through the Bible—the consistent theme from the Old Testament through the New Testament?" More than likely he won’t know. So say, "The Old Testament was God’s promise that He would destroy death. The New Testament tells how He did it." Then appeal directly to the conscience by asking if he has kept the Ten Commandments. See John 4:7–26 and 2 Timothy 3:16 footnotes.