It is in the precincts of Jerusalem, then, that punishments will be inflicted upon those who undergo the process of purification, who have received into the substance of their soul the elements of wickedness, which in a certain place is figuratively termed “lead,” and on that account iniquity is represented in Zechariah as sitting upon a “talent of lead.” But the remarks which might be made on this topic are neither to be made to all, nor to be uttered on the present occasion; for it is not unattended with danger to commit to writing the explanation of such subjects, seeing the multitude need no further instruction than that which relates to the punishment of sinners; while to ascend beyond this is not expedient, for the sake of those who are with difficulty restrained, even by fear of eternal punishment, from plunging into any degree of wickedness, and into the flood of evils which result from sin. The doctrine of Geenna, then, is unknown both to the diagram and to Celsus: for had it been otherwise, the framers of the former would not have boasted of their pictures of animals and diagrams, as if the truth were represented by these; nor would Celsus, in his treatise against the Christians, have introduced among the charges directed against them statements which they never uttered instead of what was spoken by some who perhaps are no longer in existence, but have altogether disappeared, or been reduced to a very few individuals, and these easily counted. And as it does not beseem those who profess the doctrines of Plato to offer a defence of Epicurus and his impious opinions, so neither is it for us to defend the diagram, or to refute the accusations brought against it by Celsus. We may therefore allow his charges on these points to pass as superfluous and useless, for we would censure more severely than Celsus any who should be carried away by such opinions.
Source: Against Celsus (New Advent)