On the present occasion, however, it is not our object to enter into an explanation of the subject of intelligent and sensible beings, nor of the manner in which the different kinds of days were allotted to both sorts, nor to investigate the details which belong to the subject, for we should need whole treatises for the exposition of the Mosaic cosmogony; and that work we had already performed, to the best of our ability, a considerable time before the commencement of this answer to Celsus, when we discussed with such measure of capacity as we then possessed the question of the Mosaic cosmogony of the six days.
We must keep in mind, however, that the Word promises to the righteous through the mouth of Isaiah, that days will come when not the sun, but the Lord Himself, will be to them an everlasting light, and God will be their glory. And it is from misunderstanding, I think, some pestilent heresy which gave an erroneous interpretation to the words, “Let there be light,” as if they were the expression of a wish merely on the part of the Creator, that Celsus made the remark: “The Creator did not borrow light from above, like those persons who kindle their lamps at those of their neighbours.”
Misunderstanding, moreover, another impious heresy, he has said: “If, indeed, there did exist an accursed god opposed to the great God, who did this contrary to his approval, why did he lend him the light?” So far are we from offering a defence of such puerilities, that we desire, on the contrary, distinctly to arraign the statements of these heretics as erroneous, and to undertake to refute, not those of their opinions with which we are unacquainted, as Celsus does, but those of which we have attained an accurate knowledge, derived in part from the statements of their own adherents, and partly from a careful perusal of their writings.
Source: Against Celsus (New Advent)