But let us look at what Celsus next with great ostentation announces in the following fashion: “And again,” he says, “let us resume the subject from the beginning, with a larger array of proofs. And I make no new statement, but say what has been long settled. God is good, and beautiful, and blessed, and that in the best and most beautiful degree. But if he come down among men, he must undergo a change, and a change from good to evil, from virtue to vice, from happiness to misery, and from best to worst.
Who, then, would make choice of such a change? It is the nature of a mortal, indeed, to undergo change and remoulding, but of an immortal to remain the same and unaltered. God, then, could not admit of such a change.” Now it appears to me that the fitting answer has been returned to these objections, when I have related what is called in Scripture the “condescension” of God to human affairs; for which purpose He did not need to undergo a transformation, as Celsus thinks we assert, nor a change from good to evil, nor from virtue to vice, nor from happiness to misery, nor from best to worst.
For, continuing unchangeable in His essence, He condescends to human affairs by the economy of His providence. We show, accordingly, that the holy Scriptures represent God as unchangeable, both by such words as “You are the same,” and I change not; whereas the gods of Epicurus, being composed of atoms, and, so far as their structure is concerned, capable of dissolution, endeavour to throw off the atoms which contain the elements of destruction. Nay, even the god of the Stoics, as being corporeal, at one time has his whole essence composed of the guiding principle when the conflagration (of the world) takes place; and at another, when a rearrangement of things occurs, he again becomes partly material. For even the Stoics were unable distinctly to comprehend the natural idea of God, as of a being altogether incorruptible and simple, and uncompounded and indivisible.
Source: Against Celsus (New Advent)