I got this question from a friend yesterday that went something like this: "I was asked today how I could reconcile the picture of God in the Old Testament with God in the New Testament. The question was along the lines of why God is vindictive and punishing in the Old Testament and yes forgiving and loving in the New Testament."
Certainly God is forgiving and loving in the Old Testament too (e.g., the story of Jonah, God sparing Israel) and God judges with punishment in the New Testament (e.g., Ananias and Sapphira; final judgment). But I don't think we can completely deflect this observation. In Joshua and Numbers, God has Israel in effect try to commit genocide down to children and even animals. In Ezra God commands Israelite men to divorce their non-Israelite wives and children. There are puzzling things in the OT from a Christian standpoint.
There are also things like the stoning of a man for gathering sticks on the Sabbath (Saturday). Remember that strange story at the beginning of Exodus where God tries to kill Moses until Zipporah quickly circumcises his son? Moses intercedes for Israel like you would someone almost out of control trying to beat someone else up. God is sorry he created humanity just before the Flood--not possible if God is omniscient. God sits in council with the gods of the other nations in Psalm 82, having assigned them to those nations in the first place in Deuteronomy 32--sounds like Zeus in the Lightning Thief.
A point of growth here, in my opinion, is to realize that every word of the Bible is "incarnated" revelation. God reveals himself in the categories of those to whom He reveals himself. And why not? This makes perfect sense if He wants to be understood! If God revealed himself in my categories, then no one would have really understood Him in the Bible until now, when people started looking at the world through contemporary categories.
Strangely, that's how we often treat the Bible. When we say, "God revealed the Bible as timeless, absolute truth for all time," we are really saying, "God revealed the Bible in my categories, which are the same as the categories of everyone else who has ever lived." However, this is not true. The paradigms of other times and places have differed wildly from my Western categories. The person who wants the Bible to give revelation that is unparticular to the times of its original audiences is certainly unaware of how differently those of other times and places have understood the world. Myopically, we make our time the time finally when the Bible can be understood properly, which of course is wrong and rather inadvertently self-centered.
Some will remember those denominations who used to make a distinction between infallibility and inerrancy by saying that infallible meant the Bible was without error in matters of faith and doctrine, but not necessarily science or history. This was naive, for the nature of thought and language--as I have just been saying--is for all of it to be incarnated, to take on the flesh of its time. It is thus misguided to try to consider the biblical revelation transcendent, removed from human categories, in some areas and time-conditioned in others, even in those areas related to God himself.
The necessary corollary is that even the picture of God in the Old and New Testaments is time-conditioned in the sense that it relates directly to the categories of their day. Frankly, this becomes true of the "revelations" we find in the Nicene Creed as well, meaning that theology must forever be represented in new categories, realizing that my current categories are not absolute either.
It is no surprise to me, therefore, that the Old Testament is by and large more henotheistic than purely monotheistic, meaning that God is treated as the only legitimate God to worship, though not as the only God. God also cannot change His mind if He is omniscient, meaning that I find open theism naive. I will say also that I am equally perplexed by Wesleyan-Arminians who vigorously oppose it. You you have to be conservative to be an open theist because it takes the OT picture of God very literally--more literally in fact than its opponents. It also is not process theology, as some confuse it. I understand why Calvinists would oppose it, because it emphasizes free will to the exclusion of God's determinism. But why Wesleyan-Arminians have gotten up in arms about it seems likely because of ignorance on their part.
In the end, the biblical images of God must be integrated with each other and organized from a theological fulchrum point outside the text just as all other biblical teaching. A friend of mine has as his fundamental hermeneutic "What does this text tell me about God?" This is a wonderful lens for appropriating Scripture. And we must, as with all biblical teaching, also recognize that no one biblical passage has autonomy on the answer. It is what the Bible as a whole has to tell us about God, processed through the rule of faith as encapsulated in the consensus of Christian faith, that is determinative--not the localized, time-conditioned picture of God presented by an individual passage.