Notwithstanding the fact that I do not believe in the existence of God, the Christian will make many claims about His nature all the same, but even a cursory glance at these claims leads one to the conclusion that these claims are contradictory, rendering the existence of the Christian God utterly redundant.
Apart from the 'omnis' - presence, benevolence and knowing - the claim that He is also unchanging is prevalent within Christian thought. Indeed, what use an omni-God that requires the utility of changing His mind? That would entail that those matters on which His mind has been changed were, in some manner, incorrect or ill-conceived. So it is, then, that such an omni-God must be unchanging.
With this in mind, why would God do any of the following?
Create a new covenant with humanity?.
The New Testament is touted as just such an enterprise, but it suggests that the old covenant with the Jews was not sufficient. If this be the case, why did the old covenant not encompass humanity as a whole? God's chosen people would have no need to have carried out the numerous and heinous genocides that are rampant in the Old Testament, as all of humanity would have been seen as allies - regardless of their sinful nature. Are we all not sinners regardless of whether or not one is a Christian or Jew?
Change the Ten Commandments?
The Old Testament has no fewer than three different versions of the Ten Commandments. Each of them differ. The ones espoused by modern day Christians reflect the original tablets given to Moses, but in another part of the Bible these commandments are slightly different. More worrying still, after these original commandments had been set in stone and smashed by Moses in a fit of pique regarding the construction of a golden calf, God once again called upon Moses to receive another set.
It is this set of commandments that were placed in the Ark of The Covenant and are the only ones that have the biblical subtitle of 'Ten Commandments' in our oldest manuscripts. However, they are quite distinct from those commandments first given to Moses as can be seen here. If God is unchanging, why would His commandments display so much diversity?
Is slavery still permissible?
Given that if God is genuinely unchangeable, the new covenant is clearly a forgery (or perhaps the work of Satan?), and the old covenant as set forth in the Old Testament is still in force to this day. The Old Testament gives clear instructions on how slaves are to be treated in the 613 Mosaic laws allegedly shared with him at the same time as he received the initial Ten Commandments and that would mean that Christians could conceivably still practice slavery without bruising their morality: God wants us to treat slaves in a certain way.
It could be argued that, just as the Ten Commandments were rewritten, the other Mosaic laws were also rewritten at a latter date. Just that these updated laws were not added to today's scripture. But there still lies the problem that if the Bible be an accurate account of the times of Moses then God would still have to have changed his mind with regard to slavery. This does not instil much confidence in the claim that he is unchanging.