When some people hear the biblical teaching that God “chose us in [Christ] before the foundation of the world” (Eph 1:4) and that “he predestined us for adoption to sonship through Christ,” (Eph 1:5) they think it means that God picked who would and would not be in Christ before the foundation of the world. They think Paul is saying “God chose us individuals – and not other individuals – to be in Christ from the foundation of the world.” This of course implies that some people are born predestined for heaven while all others are born predestined for hell. This is not only a nightmarish thought; it runs directly counter to the repeated emphasis in Scripture that God’s very nature is love and that he loves everybody and wants everyone to be saved.
Thankfully, this is not at all what Paul means with his language about being “chosen before the foundation of the world.”
It’s important to remember that when ancient Jews spoke about God choosing people, they thought primarily of their nation, not individuals. God chose Israel as a nation to be his “chosen people.” Yet, individuals had a choice as to whether or not they wanted to be part of this corporate election, as Paul elsewhere explicitly teaches (Rom 11). So when Paul says that “God choose us” in Christ, he doesn’t mean “God choose us individuals to be in Christ, as opposed to other individuals he didn’t choose.” What he means is “God choose all of us who are now in Christ.”
What God decided for us ahead of time was not whether we’d be in Christ or not. What he decided ahead of time was what would happen to all who chose to be in Christ. God determined that whoever chooses to be in Christ would be adopted as children and would be “holy and blameless in his sight” (Eph 1:4-5). Now that we are in Christ, what was predestined for this group before the foundation of the world applies to us.
Imagine it like this. Suppose I’m teaching a college class in which I show a certain boring documentary. After the documentary, a student asks me; “Dr. Boyd, when did you decide we’d have to watch this boring documentary?” I reply, “I decided this class would watch this boring documentary six months ago when I put together the syllabus.” The student could then turn and announce to all who were present, “Professor Boyd decided six months ago that we’d have to sit through this boring documentary.”
But notice this: I didn’t decide six months earlier that any particular student would watch – or not watch – the documentary. What I predestined was that whoever chooses to be in my class would watch this documentary. My decision was about the class, not the future individuals who would end up comprising this class. It was up to each student to decide whether what was predestined for the class was also predestined for them. Now that all these particular students had chosen to belong to my class, they could all say; “Dr. Boyd decided six months ago that we would watch this documentary.”
Whenever Paul talks about predestination “in Christ,” this is what he means. From the start God’s heart was set on humanity being incorporated “in Christ.” God committed himself to making sure – predestining – that all who would be in Christ would be called, made holy and blameless, justified, and eventually “conformed to the image of Christ” (cf. Rom. 8:29-30). But God didn’t predetermine which individuals would and would not belong to this “in-Christ” class of people.
God wants everybody to be in Christ and Jesus died for everybody to end up being in him (Jn 2:2). But since God is not a coercive God, and since love must necessarily be chosen, people have the ability to resist God’s will and the pulling of the Spirit, if they so choose.
 This seems to be what Paul means when he says “those whom God foreknew he also predestined to be conformed to the image of is Son” (Rom. 8:29), for the biblical concept of “knowing” denotes affection, not mere intellectual knowing. He uses the term “foreknow” in this same sense in Rom. 11:2.
 Even though God is omnipotent, the Bible shows us thousands of examples of people being able to resist God’s will for their lives (e.g. Lk 7:30). See Is God to Blame?.