The debate over predestination is not about the destination. It's when God decide the destination of the saved.
What really drives the idea that one's predestination starts when one is saved and is placed "in Christ" (Eph 2:13) is that
now believers are known by God, i.e.: those who never loved God before they were saved (Gal 4:8-9, 1 Cor 8:3).
Gal 4:8 But then, indeed, not knowing God, you served as slaves to those not by nature being gods.
Gal 4:9
But now, knowing God, but rather are known by God, how do you turn again to the weak and beggarly elements to which you again desire to slave anew?
Did God decide before heaven and earth were created that He would assign a destiny to those He saved when He saved them?
There is no passage I know of that says that we were predestined in eternity past. Eph 1:4 says that God
chose us "in Him" but we must never make the mistake to conflate election and predestination. They mean different things, hence they're different words.
Did God decide before heaven and earth were created that He would assign a destiny to those He saved before He saved them?
There is no passage that I know of that says that.
Did God assign a destiny to each individual who He saves, or did He assign a destiny to the category of people known as the "saved"?
Were the Ephesians ever referred to as a category in the Bible? Please forward that passage.
That is the debate.
So, as is so often the case in the Arm v Cal debate, a marked failure in understanding the issue and a complete lack of understanding the monergist position has occurred. The only reason monergists say anything about salvation being predestined for salvation is because only ones with a heavenly inheritance, those conformed to the image of Christ, and those adopted are those who are also saved. being saved and all those things to which we're predestined go hand in hand and are NEVER separated from one another.
Who wants to separate one's heavenly inheritance, conformity to the image of Christ, and adoption from one another? I don't.
Perhaps most sadly though is the fact one very important verse was left out of the list of things to which we have been predestined.
1 Thessalonians 5:9-10
For God has not destined us for wrath, but for obtaining salvation through our Lord Jesus Christ, he died for us so that, whether we are awake or asleep, we may live together with Him.
The Greek word used is εθετο which does not translate to predestinate. It translates better to appoint or to place.
1 Th 5:9
For God hath not appointed (εθετο) us to wrath, but to obtain salvation by our Lord Jesus Christ, (KJV)
To consider the meaning of the Greek poorizo a person should also consider verses like Acts 4:27-28
Acts 4:27-28
In fact, this is the very city where Herod and Pontius Pilate conspired with the Gentiles and the people of Israel against Your holy servant Jesus, whom You anointed. They carried out what Your hand and will had decided beforehand. (poorisen)
God had decided beforehand that Herod and Pilate would conspire with the Gentiles and people of Israel. When did He decide that? Did God decide that at some point during Herod's life after Herod was born? Maybe some time while Herod was in utero? Perhaps at the birth of Christ when his father murdered all those babies? Or maybe during the days of Jeremiah when he spoke of Ramah? Or perhaps it was that evening in Egypt when God first sent the angel of death to kill the firstborn in foreshadowing of Christ's death.
Now you're expanding the scope of the OP from a saved individual's predestination to Jesus' Predestination, as the Lamb slain from the foundation of the world.
Rev_13:8 And all dwelling on the earth will worship it, those whose names have not been written in the Book of Life of
the Lamb slain, from the foundation of the world.
Or maybe it was prior to Genesis 1:1.
Remember: it was those foreknew that He also predestined (Rom. 8:29). When did He foreknow a person? Well, if Jesus is any indication, then the answer lies in 1 Peter 1:20, which says Jesus was foreknown before the creation of the world. Of course, Jesus is pre-existent and we mortal humans are not, but the verse still indicates God's foreknowledge precedes creation. If we say his "fore" knowledge come after some point in history, then we must make sure the doctrine doesn't make God acting on contingency because that would subordinate the Creator to creation. We speak God’s wisdom in a mystery, the hidden wisdom which God predestined before the ages to our glory.
Now you're expanding the OP to God's foreknowledge. Nobody said God's foreknowledge comes after some point in history. For example, one's election is based on the foreknowledge of God (1 Pet 1:1-2). In the case of the Diaspora of 1 Peter, they were dispersed to that part of the world because God foreknew that they would play a vital role at that time and place.
1 Pet 1:1 Peter, an apostle of Jesus Christ, to the
elect sojourners of the Dispersion of Pontus, of Galatia, of Cappadocia, of Asia, and of Bithynia,
1 Pet 1:2
according to the foreknowledge of God the Father, in sanctification of the Spirit, to obedience and sprinkling of the blood of Jesus Christ. May grace and peace be multiplied to you.
Now back to the topic, when does one's predestination start?
