For what it’s worth, PM, Arminius NEVER left Calvinism. He remained a professor of it at Leiden(?) his entire life. He always claimed to adhere to it. Essentially, he believed his appeal to the foreknowledge of God was in such a way that it did not go out of the bounds of God’s sovereignty.
The weakness of the foreknowledge position is that it still has you choosing Him even if it was before the creation. Therefore, you’re saved not by grace but by your good sense to figure it out and choose correctly.
The weakness of the foreordination position is that it is hard to conceive how God is not the author of sin when He foreordains all, but the foreordained creature retains personal responsibility for their foreordained behavior. It’s hard to see how someone is morally responsible for preprogrammed behavior.
So Arminius was not an Arminian.
IIRC Arminus’ theology was consistent with the Heidelburg Confession but not with the more strict Calvinist positions as set forth in the Westminster Confession.
FWIW-My views on Arminius has soften over the years. I'm not quite sure if he understood the error that he was portraying - the results of what you're seeing with the "I have decided..." It is extremely subtle. Even Augustine taught this until he was confronted by the Reformed Cyprian with the question, "What do you have that you have not been given?" It was this question that made Augustine burn his writings (not a small feat in those days) and linked "free will" with Pelagius. I personally believe that Arminius was dupe by the counter-Protestant fraction of the time, but there is no proof of this except that he never left Calvinism.
It’s hard to see how someone is morally responsible for preprogrammed behavior.
Yes, I agree. But Adam would never know what love truly is while he was in the garden where he was surround by love. It was only when it was no more that he knew what he'd lost. And we know this grieved the Father to have to show Adam this for He tells us that it "grieved Him that He made man" in Gen 6. Not that God was sorry about His creation but the road to Calvery was just as hard on God as it was on us as difficult as that is to understand.
We are God's children and He is our Father in a very real sense of the term.