There are two prevalent and growing heresies relating to the undermining of the immutability of God that we should all be aware of.
Process Theology and Open Theism are kindred beliefs that begin with the fundamental thesis that reality is changing. All reality. And so, God is changing. There is an interdependance in all of reality and so God is dependant on other reality and must change in response to those other realities. God is in process, processing new situations and knowledge as they come into being.
Those who promote these beliefs say that they do not deny that God is all-powerful and sovereign and that He can ordain and control future events, He just chooses not to do so and leaves the future open to the choice of man. They say God is all-knowing but the future does not exist yet so God cannot know it yet. God, for example only knows all that can be known at the moment. So, God responds and has to change plans due to the changes in history as it unfolds.
Some of these thoughts may not seem to be that radical and it is in it’s subtle undermining of the character of God that these beliefs can be successful. It is an undermining and in many statements, an outright denial that God is in fact all-knowing of the past, present, and future as scripture clearely declares Him to be. It is a denial of the sovereignty of God and the biblical statements that He does have an immutable and eternal plan that He is working out in time. It is a denial of the infinity of God and the perfection of God. Matt Slick, serving with the Christian Apologetics & Research Ministry explains:
In Open Theism God can make mistakes because He does not know all things that will occur in the future . . . If God cannot know the future, then does it not follow logically that God is limited by time, the very thing He created? According to them, God also takes risks and adapts to the free-will choices of people. . . God can change His mind on issues depending on what He learns and what He discovers people do. Usually, God's change of mind is due to Him being surprised by something for which He didn't plan or expect. . . . My opinion is that openness is a dangerous teaching that undermines the sovereignty, majesty, infinitude, knowledge, existence, and glory of God and exalts the nature and condition of man's own free will. . . . This is absolutely and definitely a reduction in the quality, nature, and majesty of God. It is a bedrock for further heresy. And only time will tell what sort of depraved and twisted lies will come out of that fertile ground of heresy. (Excerpts from several pages at http://www.carm.org/open-theism)
Note: For a more complete and excellent study on Open Theism, please see http://www.carm.org/open-theism or the book, What Does God Know and When Does He Know It? The Current Controversy over Divine Foreknowledge by Millard Erickson
Next (72) The Immutability of God - Conclusion