Lynn H. Cohick writes on Ephesians in the NICNT series (page 143) on Chapter 2, verses 1-3:
Paul begins a new topic in Eph 2, though one that is tightly related to his previous declaration of Christ’s complete sovereignty over all powers and authorities… Paul sets before the Ephesians two sharply contrasted visions: that of the victorious and risen Christ, head of his body, the church, (1:22-23), and themselves as morally bankrupt and spiritually dead…
The New International Commentary on the New Testament
This is not how I would express it.
Yes, Paul elaborates a great deal on what he has said before. But to call it a “new topic” undercuts (in my opinion) just how “tightly related” it really is.
Paul has already mentioned the Ephesians’ trespasses and the provision for redemption and forgiveness (1:7). He also does not simply present Christ as exalted in the previous section of the letter to 2:1. After all, even to mention “the victorious and risen Christ” presupposes a previous state. Victorious over what? Risen from what? We all know the answer: God “raised him from the dead…” and highly exalted him (1:20). Paul began his prayer in 1:3 praising God for the ascension and enthronement of Christ. 1:20-23 rehearses the story of how Jesus arrived in such a place and why his exaltation includes believers. Thus, the “contrasted visions” have already been introduced before 2:1 in the contrast between Christ as corpse and Christ and resurrected Lord.
2:1-7 then is an elaboration of that story. Christ died and was raised and, in undergoing that transfiguration, he “scooped up” if you will, humanity with him. He died because we were dead. We now live, if we believe in Christ our head and representative, because we have his new life with him.
Paul basically rehearses the story of the death, resurrection, and enthronement of Jesus twice, (1:20-23; 2:1-10). Perhaps reading the text without a chapter break will make this more obvious:
I do not cease to give thanks for you, remembering you in my prayers, that the God of our Lord Jesus Christ, the Father of glory, may give you the Spirit of wisdom and of revelation in the knowledge of him, having the eyes of your hearts enlightened, that you may know what is the hope to which he has called you, what are the riches of his glorious inheritance in the saints, and what is the immeasurable greatness of his power toward us who believe, according to the working of his great might that he worked in Christ when he raised him from the dead and seated him at his right hand in the heavenly places, far above all rule and authority and power and dominion, and above every name that is named, not only in this age but also in the one to come. And he put all things under his feet and gave him as head over all things to the church, which is his body, the fullness of him who fills all in all. And you were dead in the trespasses and sins in which you once walked, following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of disobedience among whom we all once lived in the passions of our flesh, carrying out the desires of the body and the mind, and were by nature children of wrath, like the rest of mankind. And God, being rich in mercy, because of the great love with which he loved us, even when we were dead in our trespasses, made us alive together with Christ—by grace you have been saved and raised us up with him and seated us with him in the heavenly places in Christ Jesus, so that in the coming ages he might show the immeasurable riches of his grace in kindness toward us in Christ Jesus.
Ephesians 1:16-2:7 ESV (with marginal reading of v. 4)
Then, in 2:11-22, Paul elaborates the story a third time.