He thinks, besides, that those who support the cause of Christ by a reference to the writings of the prophets can give no proper answer in regard to statements in them which attribute to God that which is wicked, shameful, or impure; and assuming that no answer can be given, he proceeds to draw a whole train of inferences, none of which can be allowed. But he ought to know that those who wish to live according to the teaching of sacred Scripture understand the saying, “The knowledge of the unwise is as talk without sense,” and have learned “to be ready always to give an answer to every one that asks us a reason for the hope that is in us.” And they are not satisfied with affirming that such and such things have been predicted; but they endeavour to remove any apparent inconsistencies, and to show that, so far from there being anything evil, shameful, or impure in these predictions, everything is worthy of being received by those who understand the sacred Scriptures.
But Celsus ought to have adduced from the prophets examples of what he thought bad, or shameful, or impure, if he saw any such passages; for then his argument would have had much more force, and would have furthered his purpose much better. He gives no instances, however, but contents himself with loudly asserting the false charge that these things are to be found in Scripture. There is no reason, then, for us to defend ourselves against groundless charges, which are but empty sounds, or to take the trouble of showing that in the writings of the prophets there is nothing evil, shameful, impure, or abominable.
Source: Against Celsus (New Advent)