I’ll summarize the basic arguments they provide and give some thoughts:

Firstly, they state that the distinction between the decretive will and the moral will is a theological convention without any basis in the scriptures. The passages Calvinists use can’t show that the distinction actually exists.

I’ve never been a fan of the language and choose more specific terms for the ideas:

“Sovereign decretive will, the will by which God brings to pass whatsoever He decrees. This is hidden to us until it happens.”

This is where we agree, the other two are ambiguous.

God’s precepts- are the commands given to men to live by. We can categorize these differently from other biblical concepts. This is my replacement for the prescriptive will or what we refer to as the revealed will.

http://spirited-tech.com/2017/03/27/3-categories/

I actually don’t understand the rejection of such a notion from their perspective. They agree that God can cause events to occur. There is an obvious distinction between an event caused to happen and an event that should have happened. That’s true on their own worldview.

They state that they also believe that God has plans. This is where they and the Calvinists agree. We disagree over the nature of these plans. For Calvinists, God has a plan for creation and the creation follows that plan accordingly. In the Open Theists’ perspective, God plans things, but his plans are mutable and contingent. They are not comprehensive of the creation throughout time. The cross on this perspective is a planned event, but it also may not come to pass. Christ may die some other way and God would merely manipulate circumstances to achieve his ends. God didn’t cause such evil things to occur, but rather manipulated things for it to occur. 

The problem is that God states that he was causing these events and these people to do these things, Acts 4 states:

27 for truly in this city there were gathered together against your holy servant Jesus, whom you anointed, both Herod and Pontius Pilate, along with the Gentiles and the peoples of Israel, 28 to do whatever your hand and your plan had predestined to take place.

^{Acts 2:23} this Man, delivered over by the predetermined plan and foreknowledge of God, you nailed to a cross by the hands of godless men and put Him to death. 

The point is that even the evils of the various agents were a part of God’s plans. This couldn’t be something merely planned in the time of the first century on God’s part. God had set up parameters in the OT messianic prophesies (Daniel’s 70 weeks, Psalms 22, Isaiah’s suffering servant, etc). How could God know thousands of years in advance that these people would exist in order to play their role’s in these plans? If God didn’t predestine these individuals, then why suppose that he would get the same results with a random group of agents? 

^{Eph. 3:11} This was in accordance with the eternal purpose [purpose of the ages] which He carried out in Christ Jesus our Lord, 

Notice that in Paul’s mind the purpose of creation is the events of the cross and its results. This is paralleled to the thought a few sentences prior:

 ⁹ and to enlighten all people as to what the plan of the mystery is which for ages has been hidden in God, who created all things;

I wish to also note the common relationship with the language of foreknowledge, predestination, planning, and the like with creation language. This further suggests that the notion of the “decree” is tied with being prior to creation. In the Open Theists scheme, Christ’s death can’t be the purpose of creation because there was no guarantee that Adam and Eve would fall.

They ask how can humans make plans if God is immutably decreeing them to have plans. The problem is nonexistent for us. They merely suppose that people can’t make morally relevant choices without LFW. That is one of the contentions of the debate. So, they have a conclusion in search of an argument. We also have Psalm 33 discussed:

⁶ By the word of the Lord the heavens were made,
And by the breath of His mouth all their lights.
⁷ He gathers the waters of the sea together as a heap;
He puts the depths in storehouses.
⁸ Let all the earth fear the Lord;
Let all the inhabitants of the world stand in awe of Him.
⁹ For He spoke, and it was done;
He commanded, and it stood firm.
¹⁰ The Lord nullifies the plan of nations;
He frustrates the plans of peoples.
¹¹ The plan of the Lord stands forever,
The plans of His heart from generation to generation.
¹² Blessed is the nation whose God is the Lord,
The people He has chosen for His own inheritance.

The thing that should be most understood is that the Bible contrasts these things, but according to Open Theists there is nothing to contrast here. God’s plans are just like that of human plans in these regards. They may be frustrated and they may even be nullified and something else might need to be thought of. 

There was also the claim that 2 Peter 3:9 shouldn’t be translated as “not willing for any to perish” but rather ” not planning for any to perish”. Does he really think that God didn’t plan on anyone to perish? Why does God plan things that are obviously not going to occur? Furthermore, there was no reason cited for understanding it as God’s planning. If universalism is true, then it makes sense for God to plan for none to perish. Do they suppose that God will save everyone?  

The Open Theist side states on Eph. 1:11 that we should understand that God “works” in or with “all things” because God doesn’t cause evil things to occur.  I obviously don’t or wouldn’t accept such an assumption. He merely assumes that certain aspects of reality aren’t determined by God to be what they are. For more on Eph. 1:11, I recommend prior articles:

http://spirited-tech.com/2019/01/23/god-isnt-open/

⁸ “Remember this, and be assured;
Recall it to mind, you wrongdoers.
⁹ Remember the former things long past,
For I am God, and there is no other;
I am God, and there is no one like Me,
¹⁰ Declaring the end from the beginning,
And from ancient times things which have not been done,
Saying, ‘My plan will be established,
And I will accomplish all My good pleasure’;
¹¹ Calling a bird of prey from the east,
The man of My purpose from a distant country.
Truly I have spoken; truly I will bring it to pass.
I have planned it, I will certainly do it.

God directing the audience to look back through the entire span of Jewish history to recall the reliability of Yahweh. From the beginning of time (Gen 1), through the Patriarchs, Exodus, and all the way to the time of Isaiah. 

Rather than spelling out a long list of specific things God has done (as in 44:24-28), a general principle is explained that covers all his actions. In stark contrast to the idols that cannot even speak, much less tell the future (46:7), God is “the one who declares” (the participle ; NIV, “make known”) what has not yet happened, as well as what he will accomplish in the end. This refers to his revelation of future events to people. He is “the one who says” (the participle ) something and it happens (Gen 1 illustrates this point). There should be no doubt about his future plans, for his purposes will be accomplished;656 he does everything that he pleases. This correlation between his plans and what happens proves God’s faithfulness and reliability.

Smith, Gary V.. The New American Commentary – Isaiah 40-66: 15B (Kindle Locations 7226-7232). B&H Publishing. Kindle Edition.

^{Matt. 10:29} Are two sparrows not sold for an assarion? And yet not one of them will fall to the ground apart from your Father. ³⁰ But even the hairs of your head are all counted. ³¹ So do not fear; you are more valuable than a great number of sparrows.

The Open Theists state this is wisdom literature and shouldn’t be used as some didactic text, but they fail to give any meaning behind these words and didn’t address the a fortiori argument. If God stands behind these incidental parts of life, then why couldn’t he be behind these other parts of life?

The third reason for not being afraid is an a fortiori argument: If God’s providence is so all-embracing that not even a sparrow drops from the sky apart from the will of God, cannot that same God be trusted to extend his providence over Jesus’ disciples? The sparrow was used for food by very poor people. Two might be sold for “a penny” (one-sixteenth of a denarius, which was about a day’s wage; cf. Deissmann, Light from the Ancient East, 272– 75). “Your Father” adds a piquant touch: this God of all providence is the disciples’ Father. God’s sovereignty is not limited only to life-and-death issues; even the hairs of our heads are counted. Jesus’ third argument against fear is thus the very opposite of what is commonly advanced. People say that God cares about the big things but not about little details. But Jesus says that God’s sovereignty over the tiniest detail should give us confidence that he also superintends the larger matters.

Carson, D. A.; Carson, D. A.. Matthew (The Expositor’s Bible Commentary) (Kindle Locations 9867-9874). Zondervan. Kindle Edition.

Another argument they used was in Jeremiah 19:5, which states:

This is difficult to understand what the Open theists are claiming about the passage. It seems that because the word “decree” appears they are confusing it with the theological notion of the eternal decree. But this is talking about God’s moral commands revealed in his verbal acts and prior written revelations. God never commanded them to do such things. Furthermore, what does it mean in their view that it never even entered his mind? Do they take it to mean he never thought of it? Is God unaware of these evil possibilities? 

An argument for Divine Determinism from Creatio ex Nihilo: