In the next place, wishing to shake the faith of those who believe in Jesus on the ground of the prophecies which were delivered in regard to Him, Celsus says: “But pray, if the prophets foretold that the great God— not to put it more harshly— would become a slave, or become sick or die; would there be therefore any necessity that God should die, or suffer sickness, or become a slave, simply because such things had been foretold? Must he die in order to prove his divinity? But the prophets never would utter predictions so wicked and impious.
We need not therefore inquire whether a thing has been predicted or not, but whether the thing is honourable in itself, and worthy of God. In that which is evil and base, although it seemed that all men in the world had foretold it in a fit of madness, we must not believe. How then can the pious mind admit that those things which are said to have happened to him, could have happened to one who is God?” From this it is plain that Celsus feels the argument from prophecy to be very effective for convincing those to whom Christ is preached; but he seems to endeavour to overthrow it by an opposite probability, namely, “that the question is not whether the prophets uttered these predictions or not.”
But if he wished to reason justly and without evasion, he ought rather to have said, “We must show that these things were never predicted, or that those things which were predicted of Christ have never been fulfilled in him,” and in that way he would have established the position which he holds. In that way it would have been made plain what those prophecies are which we apply to Jesus, and how Celsus could justify himself in asserting that that application was false. And we should thus have seen whether he fairly disproved all that we bring from the prophets in behalf of Jesus, or whether he himself is convicted of a shameless endeavour to resist the plainest truths by violent assertions.
Source: Against Celsus (New Advent)