Verse 1: Paul, an apostle of Jesus Christ by the will of God, to the saints which are at Ephesus, and to the faithful in Christ Jesus: Notice that he says that they are in Christ Jesus. In this book, Paul's focus is who we are in Christ. Some have made an attempt to prove that Paul is addressing two different group of people in this letter, i.e., the saints in Ephesus and the faithful in Christ Jesus. I have ran that route to its logical conclusion and disagree. Paul was the apostle to the Gentiles and wrote to the Body of Christ in his epistles, and we he does address the Jewish nation specifically, he makes it obvious. Also, I have found that those who go down that rabbit hole will find themselves in a ditch very quickly when they carry that method into Paul's other letters.
Verses 2-3: Grace be to you, and peace, from God our Father, and from the Lord Jesus Christ. Blessed be the God and Father of our Lord Jesus Christ, who hath blessed us with all spiritual blessings in heavenly places in Christ: Notice that our blessings are spiritual and in heavenly places. When do we get these spiritual blessings? - At the moment of our salvation (1 Corinthians 12:12-13).
This chapter lists nine spiritual blessings. In 1:3-6, the Father chose us, adopted us, accepted us. In 1:7-12, the Son redeemed us, abounded toward us, gave us an inheritance. And in 1:13-14, the Holy Spirit reveals to us, sealed us, earnest of our inheritance.
Verse 4: According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: We can still have free will and God can still know who will and who will not. He is God, right? That we should be holy: Just like the tools in the temple, we have been set aside (made holy, consecrated) for His purpose. Without blame.
How are we without blame? Paul mentioned the concept in 1 Corinthians 1:7-8. We are justified from all things simply by our faith in the finished work of Christ on the cross and nothing more. The result is that we are truly blameless.
Verse 5: Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will, Keep in mind that adoption speaks of coming into full rights as an heir. It has nothing to do with anything that we have to work for. It happens at the moment of salvation. At that moment, we become joint-heirs with Christ in heavenly places (verse 3).
Regarding predestination, sad how it has been so distorted in the church today. It is not referring to whether someone is predetermined to go to heaven or hell. Instead, it speaks of our position in Christ as a joint-heir. The root of the word is destiny. It is our destiny now that we are in Christ. We have been predestined (destined) to be adopted (Romans 8:17-18) and it will be complete at the rapture.
And he says that it is according to the good pleasure of his will. The same way that Paul was called in 1:1a. John also references this in John 6:44. Also, an example of it is seen in Acts 16:14. The Lord opens the eyes of our understanding but the choice is still ours, e.g., he calls, we respond, and he chooses. Not that difficult in my opinion. Augustine and John Calvin have made a mess out of this issue.
Verse 6: To the praise of the glory of his grace, wherein he hath made us accepted in the beloved. In the beloved means in Christ. It is by grace and grace alone as he has already established.