Jamieson, Fausset and Brown on Acts 26:24

24. Festus said with a loud voice--surprised and bewildered.

Paul, thou art beside thyself, much learning doth make thee mad--"is turning thy head." The union of flowing Greek, deep acquaintance with the sacred writings of his nation, reference to a resurrection and other doctrines to a Roman utterly unintelligible, and, above all, lofty religious earnestness, so strange to the cultivated, cold-hearted skeptics of that day--may account for this sudden exclamation.