Compare this dialogue in Plato’s Republic to modern Calvinists:
And what do you think of a second principle? Shall I ask you whether God is a magician, and of a nature to appear insidiously now in one shape, and now in another–sometimes himself changing and passing into many forms, sometimes deceiving us with the semblance of such transformations; or is he one and the same immutably fixed in his own proper image?
I cannot answer you, he said, without more thought.
Well, I said; but if we suppose a change in anything, that change must be effected either by the thing itself, or by some other thing?
And things which are at their best are also least liable to be altered or discomposed; for example, when healthiest and strongest, the human frame is least liable to be affected by meats and drinks, and the plant which is in the fullest vigour also suffers least from winds or the heat of the sun or any similar causes.
And will not the bravest and wisest soul be least confused or deranged by any external influence?
And the same principle, as I should suppose, applies to all composite things–furniture, houses, garments: when good and well made, they are least altered by time and circumstances.
Then everything which is good, whether made by art or nature, or both, is least liable to suffer change from without?
But surely God and the things of God are in every way perfect?
Of course they are.
Then he can hardly be compelled by external influence to take many shapes?
But may he not change and transform himself?
Clearly, he said, that must be the case if he is changed at all.
And will he then change himself for the better and fairer, or for the worse and more unsightly?
If he change at all he can only change for the worse, for we cannot suppose him to be deficient either in virtue or beauty.
From Norman Geisler in Creating God in the Image of Man:
Briefly put, whatever changes acquires something new. But God cannot acquire anything new, since he is absolutely perfect; he could not be better. Therefore God cannot change.
God is by his very nature an absolutely perfect being. If there were any perfection that he lacked, then he would not be God. However to change one must gain something new. But to gain a new perfection is to have lacked it to begin with. Hence, God cannot change. If he did, he would not be God. Rather, he would be a being lacking in some perfection, not the absolutely perfect God that he is.
Does Mr Geisler sound more like the Bible or more like Plato? The reader can decide.