He maintains, moreover, that “no product of matter is immortal.” Now, in answer to this it may be said, that if no product of matter is immortal, then either the whole world is immortal, and thus not a product of matter, or it is not immortal. If, accordingly, the world is immortal (which is agreeable to the view of those who say that the soul alone is the work of God, and was produced from a certain bowl), let Celsus show that the world was not produced from a matter devoid of qualities, remembering his own assertion that “no product of matter is immortal.”
If, however, the world is not immortal (seeing it is a product of matter), but mortal, does it also perish, or does it not? For if it perish, it will perish as being a work of God; and then, in the event of the world perishing, what will become of the soul, which is also a work of God? Let Celsus answer this! But if, perverting the notion of immortality, he will assert that, although perishable, it is immortal, because it does not really perish; that it is capable of dying, but does not actually die—it is evident that, according to him, there will exist something which is at the same time mortal and immortal, by being capable of both conditions; and that which does not die will be mortal, and that which is not immortal by nature will be termed in a peculiar sense immortal, because it does not die!
According to what distinction, then, in the meaning of words, will he maintain that no product of matter is immortal? And thus you see that the ideas contained in his writings, when closely examined and tested, are proved not to be sound and incontrovertible. And after making these assertions he adds: “On this point these remarks are sufficient; and if any one is capable of hearing and examining further, he will come to know (the truth).” Let us, then, who in his opinion are unintelligent individuals, see what will result from our being able to listen to him for a little, and so continue our investigation.
Source: Against Celsus (New Advent)