From Dan Martin of Nailing it to the Door:
Open Theism starts–never forget this–not from logical assumptions, but from observing that the God represented in our scriptures is a dynamic, interactive God who changes his mind, his plans, and his behavior in interaction with his creatures. This is not wishful thinking and it’s not secular philosophy, it’s how the stories actually read. Open Theists simply insist that no rationalization or mental gymnastics need be applied to the Biblical accounts of God dealing with his own people.
For full post, click here.
God is Open 
Open theism = No gymnastics…. Just the plain reading of the text.
Numbers 23:19 God is not man, that he should lie, or a son of man, that he should change his mind. Has he said, and will he not do it? Or has he spoken, and will he not fulfill it?
Psalm 110:4 The Lord has sworn and will not change his mind,
Hebrews 7 Quoting Psalm 110 “The Lord has sworn and will not change his mind, ‘You are a priest forever.’” 22 This makes Jesus the guarantor of ia better covenant
Simple conclusion from the plain reading of the text, GOD does not change his mind!
-Anon
Are you reading the verses in context, using straightforward understandings?
yes. quite literally so.
God is not man that he should change his mind seems rather simple. moreover it doesn’t require any gymnastics.
Exodus 32:14 “So the LORD changed His mind about the harm which He said He would do to His people.”
Jeremiah 18:8 “if that nation against which I have spoken turns from its evil, I will [a]relent concerning the calamity I planned to bring on it.”
What’s your simple reading on those?
I get it. The goal is to rally the base, make outlandish comments such as NO mental gymnastics needed, then avoid explaining clear teachings in the bible.
To deny that God is accessible, hears prayers and even “changes”his mind would be to throw out characteristics of a God who has condescended to us in our weakness and now sits at the right hand of the Father making intercession on our behalf. What seems to be lost on you however is that there is also clear teaching in the bible that says God does not change his mind!. The claim was no mental gymnastics, it gets no clearer that God is not man that He would change His mind.
So we are left with a dilemma. My point in this was to demonstrate that you, that is the ‘open’ position must do gymnastics in order to hold to this view point.
If it was so simple, then it would have been a held and widely accepted before the 1990’s. Not the case.
Grace and peace
-Anon
Actually, the places where God is portrayed in the Bible as not changing his mind are in the context of specific decrees, so it’s not at all hard to reconcile them with these others. It’s a simple matter of context.see these two posts for more detail:
http://nailtothedoor.com/does-god-change-part-1-of-2/
http://nailtothedoor.com/does-god-change-part-2-of-2/
As to your historical claim, I leave it to people with a better command than I, but would point out that the same argument was leveled against every major reformer in the 16th & 17th centuries…