Thank you. I'm still not sure I understand how it works. I don't see how Calvinism doesn't fall off the tracks one way or the other, either into Molinism one way or robotics the other.
I am glad that Lutherans can, in no uncertain terms, say that God does not will evil to happen. Correct me if I am wrong, but these are Lutheran statements of belief that I do not think a Calvinist could agree with.
"God's foreknowledge foresees and foreknows what is evil, yet not in the sense that it is God's gracious will that evil should happen."
"The beginning and cause of evil is not God's foreknowledge, (For God does not create and do evil, neither does He help or promote it.) The cause of this evil is the wicked, perverse will of the devil and of people. (Hosea 13:9, Psalm 5:4)"
The usual answer is "compatibilism." That is, we think the God having a plan for everything is compatible with people making responsible choices. (I say responsible rather than free because the definition of free will is one of the major matters under discussion.)
I don't think that the essence of responsible choice is unpredictability. I believe that the saner and more coherent someone's decision making, the easier it would be to predict it. This can only be speculation due to my dim knowledge of God, but I would bet that if we had God's perspective on things we would find that given his character and goals, he had no choice but to do what he actually did.
Rather, the essence of responsible choice is that the choice reflects the person's character, the situation, and his goals. That someone forced him to do something diminishes responsibility, because the choice no longer reflects his own character. Insanity also diminishes responsibility, because the choice may be based on an illusion, and not the person's actual character. But the fact that someone is acting in accordance with God's plan doesn't involve either force or insanity, and doesn't diminish the fact that the person actually makes the decisions that they make, and those decisions reflect their character. [This is basically the analysis in Jonathan Edwards "Freedom of the Will"]
In most Reformed thought, God works through secondary causes. He doesn't just reach down and do things most of the time. He is responsible of the entire situation and all the people in it, and makes sure that all the parts fit together to come out according to his plan.
This means that in most cases there are two explanations of every event, both of which are true. One is in terms of God's plan, the other explains it in terms of the normal operation of intelligent agents and nature law. God uses that operation to execute his plan. [In the Institutes, Calvin gives an example where there are actually three accounts operating at the same time, because Satan is involved. People are acting in accordance with his plan. But he is unknowingly part of a more far-reaching plan by God.]
This is particularly true in the case of salvation, because the normal concept of providence -- with God responsible for everything that happens -- is joined by something more personal. The Holy Spirit is personally present in all Christians, regenerating them and enabling them to follow God's will.
(I note that I'm not necessarily describing my own beliefs of how God actually works, though I do think traditional Reformed theology's account is rational and self-consistent. Many modern Reformed thinkers have sympathies for Lutheran thought on this issue, and even open theism. But most participants here are traditional.)