E.W. Bullinger provides an interesting commentary of the letters of apostle Paul in his The Church Epistles - Romans to Thessalonians and offers some fascinating insights.
In the beginning of the book, he discusses the organization and structure of the epistles and explains how the seven books can be grouped into two sets of three and four. Romans, Ephesians and Thessalonians making the set of three, and then Corinthians, Galatians, Philippians, and Colossians making the set of four. At first I was going to attempt to provide my own interpretation but I quickly came to see that it would be more expedient simply to use his words. He goes on to explain that Romans stands first, containing the A, B, Cs of Christian education...
Until its great lesson is learnt we know nothing. If we are wrong here, we must be wrong altogether. The Spirit has placed it first because it lies at the threshold of church-teaching.
The doctrinal portion, consisting of the first eight chapters, shows what God has done with "sins" and with "sin," and how the saved sinner has died with Christ, and is risen with Christ = made a son and heir of God in Him.
This is where Ephesians starts from! It begins not with man, but with God. It approaches its great subject, not from man's necessities, but from God's purposes. It is occupied not so much with what the saved sinner is made in Christ, but with what Chris is made to be unto him. It is God's point of view rather than man's.
In Romans we have the Gospel: in Ephesians the Mystery.
In Romans the saved sinner is shown as dead and risen whit Christ: in Ephesians as seated in the heavenlies in Christ; while in Thessalonians he is seen for ever in glory with Christ.
Romans takes up the sinner in his lowest depths of degradation: and Thessalonians leaves him on "the thrown of glory for ever with the Lord": while, midway between, Ephesians views us now by faith as already seated with Him there. Our feet have been taken out of the mire and clay (Romans 1); they are now set upon the rock (Eph. 1) and presently we shall be upon the throne 1 Thess. 4).
Viewed together, they form the A, B Cs of the Christian faith, as distinct from all else in the whole Bible - nothing like it is found elsewhere. All the rest is written for us, for our learning. But this is all about us. The course of instruction is complete, and it is perfect. It commences at the lowest point and leaves us at the highest.
Looking at the second set of four books we find that they are in pairs - Corinthians and Galatians follows Romans because they exhibit departure from its special teaching. The second pair - Philippians and Colossians follow Ephesians because they exhibit departure from its special teaching.
So that we have the whole course of church teaching; the complete curriculum of Christian education, set before us as a whole, positively and negatively.
In the three (Rom., Eph., and Thess.), we have "doctrine" and "instruction". In the four (Cor., Gal., Phil., and Col.) we have "reproof" and "correction". Here is seen how "profitable" these Epistles are for the perfection (i.e., the complete education) of "the man of God", fitting him out for every duty and every emergency.
But there is a further correspondence between these four Epistles.
The first of each pair, (Cor. and Phi.) exhibits practical departure, while the second of each pair (Gal. and Col.) exhibits doctrinal departure. That is to say, in Corinthians we have practical failure as to the teaching of Romans, while in Philippians we have a failure to exhibit in practical life the teaching of Ephesians as to the unity of the members of Christ's Body.
On the other hand, in Galatians we have doctrinal failure as to the teaching of Romans. This is why Gal. and Rom. are so much alike, as everyone knows; though, all that most can see in this likeness is that they were "written about the same time"! The real difference is that what is stated as "doctrine" in Romans is repeated as "correction" in Galatians.
So in Colossians we have doctrinal failure as to the teaching of Ephesian truth. In Ephesians, Christ is revealed and set forth as "the head of the Body". In Col. we have the doctrinal evils which come from "not holding the Head" (Col. 2:19)
Given this, we have an outline "structure" as follows:
The rest of the book provides a commentary on the seven Epistles and expands considerably on the structure and content above.
What a fascinating individual Bullinger must have been to have been able to glean such insights from his study. I am continually amazed as I read his work. I haven't finished The Church Epistles - Romans to Thessalonians yet but I already know that, like some of his other work, I'll read it again a second or third time. This is definitely a must-read volume that anyone who is serious about the Bible will want to have in their library. I suspect the folks at Hearts and Minds Books would be happy to get a copy to you.