In 1984 Pinnock published an excellent book, The Scripture Principle, in which he ably defended the inerrancy of Scripture.
Later in life he became, and died, an Open Theist, a very sad example of those who come to believe that they know more than God.
He is only one of many so called "scholars" who come to believe they know more than God.
One that always comes to mind is Bishop Pile who died in
a Judean desert looking for the "historical Jesus'!
Y1, open theism does not claim that God is limited.
Instead, open theism claims that God is omniscient and unlimited, knowing all that can be known (contingencies simply are not something that qualifies as "knowable"....e.g., the idea that God can not hear the color blue does not limit God).
I disagree with open theism, but your oversimplification is problematic when debating the issue. We also have to be careful
of stating that God cannot impose limits upon Himself, or that in limiting Himself He is not really God in all of His attributes (we cannot consistently make that claim without denying the deity of Jesus).
That said, open theism is beyond the scope of orthodox Christianity.
I believe it holds to a false understanding of the mode of divine knowledge (the same as Arminianism) taken to a different and perhaps more logical conclusion.
They though tend to be stating that Gid Himself has decided to enter into his creation, to be a process within it, and so has limited Himself to just how much of the future is either foreseen/predestined!
they just deny that God has absolute sovereinghty, as to them means man has no free will at all!
God did enter into his creation, and the Word did become flesh.
I don't see contemporary Open Theists arguing that God limits himself as much as I see them arguing that future contingencies are unknowable by nature except when purposed by God.
I agree that open theism is heresy.
Originally, a "heresy" was a doctrine or practice not held by the majority. There are lots of heresies today, based on that meaning, Calvinism and PSA being two such.
I really don't like the word. It is too often used to malign others. It was used as an excuse to burn and behead by the state churches, which considered believer's baptism and religious freedom as heresies.
Paul was opposed to judaizers but did not treat them as others treated him.
Let's "observe" for this can be an instructive moment.
Acts 21
17 And when we were come to Jerusalem, the brethren received us gladly.
18 And the day following Paul went in with us unto James; and all the elders were present.
19 And when he had saluted them, he declared particularly what things God had wrought among the Gentiles by his ministry.
20 And
when they heard it, they glorified the Lord, and said unto him, Thou
seest, brother, how many thousands of Jews there are which believe; and
they are all zealous of the law:
21 And
they are informed of thee, that thou teachest all the Jews which are
among the Gentiles to forsake Moses, saying that they ought not to
circumcise their children, neither to walk after the customs.
22 What is it therefore? the multitude must needs come together: for they will hear that thou art come.
23 Do therefore this that we say to thee: We have four men which have a vow on them;
24 Them
take, and purify thyself with them, and be at charges with them, that
they may shave their heads: and all may know that those things, whereof
they were informed concerning thee, are nothing; but that thou thyself
also walkest orderly, and keepest the law.
25 As
touching the Gentiles which believe, we have written and concluded that
they observe no such thing, save only that they keep themselves from
things offered to idols, and from blood, and from strangled, and from
fornication.
26 Then
Paul took the men, and the next day purifying himself with them entered
into the temple, to signify the accomplishment of the days of
purification, until that an offering should be offered for every one of
them.
Then after an interval of fourteen years I went up again to Jerusalem with Barnabas, taking Titus along also. It was because of a revelation that I went up; and I submitted to them the gospel which I preach among the Gentiles, but I did so in private to those who were of reputation, for fear that I might be running, or had run, in vain.
But not even Titus, who was with me, though he was a Greek, was compelled to be circumcised.
But it was because of the false brethren secretly brought in, who had sneaked in to spy out our liberty which we have in Christ Jesus, in order to bring us into bondage.
But we did not yield in subjection to them for even an hour, so that the truth of the gospel would remain with you.