Thank you for asking. I am Reformed, to help in your quest for an answer, I searched and found an article from Pastor Sam Storms on crossway.org that I recommend
HERE. If I get more time, I may attempt a personalized, but partial answer.
I read the Sam Storm article on the link you provided , and I have to say I disagree with his views. Here is how I interpreted Ephesians 1,2 3 - whoch will help us to understand Romans 8 (predestine) and 1Peter 2 (chosen people) : I will give comments and questions as food for thoughts regarding Predestination in Ephesians:
Eph 1:4,5: "...He chose us in him before the foundation of the world ... he predestined us .. according to the purpose of his will"
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-- Does "us" refer to individuals who are predestined or pre-planned to be saved by God from beginning? Does God choose us individually?
-- Or does "predestined us" mean other people? This can be answered from the next 50 verses, until Ephesian chapter 3.
Eph 1:11-14 -- "[11] In him we have obtained an inheritance, having been predestined according to the purpose of him ... we who were the first to hope in Christ ... [13] In him you also, when you heard the truth and believed in him ..."
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-- Why did Paul said we and you?
--- Who were the 'we' in "we were first to hope in Christ"? The first people to believe in Jesus were Jews, isn't it?
-- Who are 'you"? Chapter 2:11-3:11 explain it abundantly.
Eph 2:11-14 Therefore remember that formerly you,
the Gentiles in the flesh—who are called “uncircumcision”.... you were at that time without the Messiah, alienated from the citizenship of Israel... [13] But now ...you...have been brought near by the blood of Christ. [14] For he ... ,
the one who made both groups into one ... ==>>
-- NIV and ESV versions said "you, the Gentiles," so 'you' referred to Gentiles. The words " upi who are called "uncircumcision" clearly means the Gentiles
- Paul was saying how Christ has bought TWO peoples. the Jews and Gentiles, together by offering salvation to both groups. This is the main theme of Ephesians.
Notice how Paul continued to emphasize God's will for Jews and Gentiles: The word
BOTH appears 3x in the following verses:
2:16-22: to reconcile them
BOTH in one body to God through the cross.... [18] so that through him
we BOTH have access in one Spirit to the Father ... you are members of the household of God,...
being joined together ==>
-- Paul was explaining how God had planned to reach out to both Jews and Gentiles, n reconciled them in Him.
Jews and Gentiles are the subjects of discussion here - God had predestined or preplanned to offer redemption to both peoples and if any Jews or Gentiles repented, they would be saved. Paul was NOT writing about individual predestination.
God's will and purpose (Ephesians 1:5,11] is explained in 3:1-11:
[3:1-6] -- In reading this, then, you will be able to understand my insight into the mystery of Christ, [5] which was not made known to people in other generations as it has now been revealed by the Spirit to God’s holy apostles and prophets [6] This mystery is that through the gospel the Gentiles are heirs together with Israel , members together of one body and sharers together in the promise in Christ
- In Ephesians chapter 1 to 3, Paul explained how Christ fulfilled the purpose of God's will, which is to reconcile BOTH Jews and Gentiles. Therefore God's will does NOT refer to His will for individual redemption ie God does not handpick Susan or Jason to be saved.
-- We all know that after Peter's vision of eating unclean food, the apostles preached to the Gentiles, much to the resentment of the Christian Jews, who had shunned the Gentiles for ages. This is what "
not known previous generations ... but mow revealed to apostles" mean.
- So what does God's will mean in context? [Eph 3] "He made known to us the
mystery of his will according to his good pleasure, which he purposed in Christ, [10] to be put into effect when the times reach their fulfilment —
to bring unity to all things in heaven and on earth under Christ.
Back to Ephesians 1:
- So now, going to Eph 1, does predestination mean that God choose individuals OR does it mean God preplanned to offer redemption to both Jews and Gentiles? The entire three chapters support the latter theme.
--
If Paul was referring to individual predestination, why would he immediately changed subjects or topic to reconciliation of both Jews n Gentiles from 2:13 to 3:13 ?
-- Eph 1:4,5,7,11 : God chose or predestined us refer to how He reached out to we the Jews first. Writing as a Jew, Paul used the word "we" and "us" as he referred to Jews [1:4,5,7]:
"We" refer to Christian JEWS such as the apostles, the earliest disciples who saw Jesus ascended to heaven, the 3000 Jews who believed during Pentecost, and other Christian Jews during apostles' generation -- broadly speaking. And as Paul referred to the audience of his letter, the Gentiles, he said "you too" or "you were also included" [13]. This explained the words "we" "us" and "you".
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Why did Paul said "chose us before the "foundation of the Earth"? As Jewish Christians resented Gentile Christians, they claimed that Jews were there first, insisting that Gentile believers had to observe Sabbath and circumcision. They would even said God in the beginning never intended to offer redemption to Gentiles, but He suddenly decided to because most of Israel did not turn to Jesus. To reject their arguments, Paul emphasized that way-way back, even before the foundation of the earth, God had already planned to offer redemption to Gentiles. Even before the earth began, God had preplanned His move, that was how EARLY it really started, don't bother arguing that it was conceived lately.
"Before the foundation of the earth" is a figure of speech to emphasize that the plan started at the earliest time anyone can think of. This also explain the word "foreknowledge"; God KNEW AHEAD - way, way ahead - that He would reached out to the Jews first, and then the Gentiles -- which together means everyone on earth, on condition that people confess their sins and ask for forgiveness in Christ.