But if he were dealing honestly in his accusations, he ought to have given the exact terms of the prophecies, whether those in which the speaker is introduced as claiming to be God Almighty, or those in which the Son of God speaks, or finally those under the name of the Holy Spirit. For thus he might have endeavoured to overthrow these assertions, and have shown that there was no divine inspiration in those words which urged men to forsake their sins, which condemned the past and foretold the future.
For the prophecies were recorded and preserved by men living at the time, that those who came after might read and admire them as the oracles of God, and that they might profit not only by the warnings and admonitions, but also by the predictions, which, being shown by events to have proceeded from the Spirit of God, bind men to the practice of piety as set forth in the law and the prophets. The prophets have therefore, as God commanded them, declared with all plainness those things which it was desirable that the hearers should understand at once for the regulation of their conduct; while in regard to deeper and more mysterious subjects, which lay beyond the reach of the common understanding, they set them forth in the form of enigmas and allegories, or of what are called dark sayings, parables, or similitudes.
And this plan they have followed, that those who are ready to shun no labour and spare no pains in their endeavours after truth and virtue might search into their meaning, and having found it, might apply it as reason requires. But Celsus, ever vigorous in his denunciations, as though he were angry at his inability to understand the language of the prophets, scoffs at them thus: “To these grand promises are added strange, fanatical, and quite unintelligible words, of which no rational person can find the meaning; for so dark are they as to have no meaning at all; but they give occasion to every fool or impostor to apply them so as to suit his own purposes.”
This statement of Celsus seems ingeniously designed to dissuade readers from attempting any inquiry or careful search into their meaning. And in this he is not unlike certain persons, who said to a man whom a prophet had visited to announce future events, “Wherefore came this mad fellow to you?”
Source: Against Celsus (New Advent)