The first thing I would affirm about Paul’s segues in general is that I believe that Paul always knows where he is going. Secondly, it is not always easy to see at the start how he is going to get where he ends up by means of what we see in the middle. Third, sometimes it is not always clear exactly how one thing relates to the next thing, but time spent thinking through the connections is not usually wasted time. Sometimes that time shows us a deep and profound organization to the whole and important relationships in the parts. Fourth and "however," the connection between the previous thing and the next thing may not always be organized as tightly as we presume it to be. Sometimes the word "for" is not as profound as we think it is.
I bet Paul sometimes just wants to change topics and uses rhetorically-conventional segues that might look more important to modern eyes than they really are. Sometimes they might be little more than a change in subjects. That would explain why occasionally it is really hard to see Paul's reasoning when he connects the last thing with the next thing he talks about. Sometimes, when the connections are not especially tight and obvious and when we have done all the thinking we can about it, Paul might be making a quasi-random jump--loosely connected to the foregoing by means of a word or concept, but ultimately just a convenient means to bring the subject back around to where he wants to go in the end or to something he wants to cover on the way. The language might make us think the dots are more connected than they really are, so we spend much time thinking through the connection, when maybe we should just recognize that Paul is using smooth rhetoric to change subjects. You know, kind of a “Speaking of spectacular dives, how ‘bout them 'Eers, huh?”
Anyway, having said that, I want to point out some transitions through four subjects in Romans 8 that remain well-connected to the overall topic of the chapter (the Spirit), but in which the chain of reasoning from one to the next is not simple to explain. When connected, the dots do not always produce a straight line, even though they definitely draw a picture. In some cases, Paul might more interested in getting to the next topic than about drawing rich connections between the topics.
First though, be aware that Chapters 6-8 are themselves a subtopic of a larger topic in Romans. In chapters 1-7, Paul has effectively argued that justification is always and only by grace through faith; we are most definitely NOT saved by keeping the law. Then in chapters 6-8, he anticipates a potential charge against what he has said--justification by faith might lead to or excuse unrighteousness. Paul argues that this is not true because 1) chapter six tells us that those who are justified have died to sin through Christ; 2) chapter 7 tells us that the law is an essential means by which people come to Christ; and 3) chapter 8 tells us that those who have been justified have the Holy Spirit, who is transforming them into actively righteous people. Paul wants this last chapter to be be all about the “Holy Spirit.” We know this because before this he has only mentioned the Spirit four or so times. In chapter 8 the Spirit suddenly shows up some 20 times.
So within the topic of the Holy Spirit, Paul moves quickly through four subtopics (justification, sanctification, adoption, and glorification). He uses what to him must have been smooth, rhetorical transitions to tie them all together under the larger topic of the Spirit. But with each transition the modern interpreter is forced to ask, “How does the aft relate to the fore, and what are the implications of the relationship?” What I am arguing though is that while it is not likely that he is being utterly random in his topic changes, neither is he always being explanatory. Sometimes we just need to accept the subject change, without “over-arcing” the relationship between the subjects.
The technique of Paul's transitions in this chapter is to write a sentence or clause that references the previous topic (the 'fore") while at the same time introducing the next topic, (the "aft"). Something smoother than, but not unlike, “Speaking of this, let’s now talk about that.”
Verses 1-4 re-introduce the sub-topic of justification which is connected to the larger chapter topic of “Holy Spirit” through the phrase “Law of the Spirit of life.” We usually see Justification as something more related in its mechanics to the work of Christ, but Paul wants us to know that it is not at all unrelated to the work of the Spirit. The phrase also serves as a transition from the previous larger topic of Law to the new larger topic of the work of the Holy Spirit, under which the four topics of this chapter reside.
So, Paul talks about justification in verses 1-3, and then he uses verse 4 to transition to sanctification. He talks about the last thing, and then introduces the next thing:
Romans 8:4 in order that the righteous requirement of the law might be fulfilled in us [justification], who walk not according to the flesh but according to the Spirit [sanctification]. (ESV)
You can see how the exact phrasing of the transition--the “who” phrase--needs some real exegetical focus to understand exactly what Paul is implying about the connection between those who are justified and those who walk according to the Spirit. However, it is possible to overthink it. The interpreter needs to consider whether this transition clause is just as much or more about simply moving to a closely related subject than trying to demonstrate a tightly explainable relationship between the two subjects. The same is true with the next two transitions:
Paul has transitioned in verse 4 from justification to the Spirit’s role in sanctification--a discussion that, if we do not understand how it is situated among the larger topics of book of Romans, could subtly and scarily lead one back into a kind of works righteousness mentality. We could get lost deep in the trees, so to speak, and lose our place in the forest. He is explaining why justification by faith does not lead to or excuse unrighteousness. But getting lost in the trees here would cause some people to waste time trying to figure out how Paul is not actually saying that the righteous requirement of the law is met only for those who actually meet the righteous requirement of the law (not living according to the flesh, but according to the Spirit). If you are not getting what I am saying, then that might be a good thing, maybe you understand him easily. Or it might mean that you are spending too much time looking at the forest and not enough time looking at the trees in this chapter. I do not want you to waste time here unnecessarily, but neither do I want you to miss the value of exegetically struggling with the text. The text needs to touch your hip so to speak, and that only happens when you wrestle with it vigorously. In the end, you should still be able to walk, but you should be limping a little. If you don't limp when you read this transition, then I suspect you didn’t wrestle enough.
At the end of the sanctification portion, Paul transitions from sanctification to adoption, once again using his “fore and aft” topic technique:
Romans 8:14 For all who are led by the Spirit of God [sanctification] are sons of God [adoption]. (ESV)
We have to understand that being led by the Spirit here is not some mystical, extrabiblical, revelatory connection to the Spirit’s guidance. It is equivalent to four other things in this sanctification section which are just as vaguely expressed: walking in the Spirit, living by the Spirit, setting the mind on the things of the Spirit, and putting to death the deeds of the flesh by the Spirit. In other words, being “led by the Spirit” is not Keswick deeper life stuff or charismatic mysticism. It is simply sanctification. If you are being sanctified, then you are sons of God. Which is the next topic.
Adoption is mentioned as a function of the larger “Spirit” topic in verses 14-17. Take note that these verses are chock full of covenantal references to the Abrahamic promises and the gentiles--a tie-in to themes in previous and later chapters. We are sons, children, and heirs. Then Paul once again almost abruptly transitions using the fore and aft technique from adoption to glorification:
Romans 8:17 and if children, then heirs—heirs of God and fellow heirs with Christ [adoption], provided we suffer with him in order that we may also be glorified with him [glorification]. (ESV)
Of all four topics/three transitions under discussion, this one is the most abrupt. The inferrable connections between the fore and aft in this one are almost brutal to wade through. The language raises a lot of questions. If you do not see those questions, then you're not staring at it hard enough. Those who preach a really tight connection between the fore and the aft, based upon the grammar underlying the words, are going to have to spend a lot of time explaining how this does not undermine justification by faith alone. I am not saying that the interpreter should ignore the connection: one can preach the difference between the means of salvation and the effect of salvation fairly easily. But sometimes Paul is just simply wanting to move from one topic to another, and does not expect us to do exegetical flip flops in order to maintain our faith-based theology.
These examples of transitions in Romans 8 need to be milked for all their implications. But one of the options when "arcing" transitional relationships should be that Paul is just "smoothly" moving on, in his eyes at least, to the next related subject that he wants to cover. I am not arguing that we should not spend time studying and “arcing” transitions and topics. Obviously everything is related and there is a richness in the relationships. But sometimes exegesis can be too much tree and not enough forest, especially in the transitions. Sometimes we can overthink it in an effort to explain it. Sometimes Paul is just finding important ways to get where he is ultimately going.