Romans and Hebrews are the two most theological epistles. One reason this is not surprising is that Romans is the only letter of Paul’s that is not tied in with running a church and/or dealing with particular congregants. What follows is definitely not an in-depth discussion of Paul’s theology, but an outline with discussion that focuses more on the nontheological emphases in the book.
Chapter 1: Paul greets and praises the Roman Christians, promises to learn from all peoples, and then slams those who don’t follow God. There’s no excuse for denying Him, for He is manifest to us all both externally and internally (this is rather how C.S. Lewis begins Mere Christianity):
18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men who suppress the truth in unrighteousness, 19 because that which is known about God is evident within them; for God made it evident to them. 20 For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse.
As for specific sins, Paul first condemns homosexual acts by both men and women (1:26-27) and then continues:
28 And just as they did not see fit to acknowledge God any longer, God gave them over to a depraved mind, to do those things which are not proper, 29 being filled with all unrighteousness, wickedness, greed, evil; full of envy, murder, strife, deceit, malice; they are gossips, 30 slanderers, haters of God, insolent, arrogant, boastful, inventors of evil, disobedient to parents, 31 without understanding, untrustworthy, unloving, unmerciful; 32 and although they know the ordinance of God, that those who practice such things are worthy of death, they not only do the same, but also give hearty approval to those who practice them.
Chapter 2: Paul continues to slam the unrighteous:
5 But because of your stubbornness and unrepentant heart you are storing up wrath for yourself in the day of wrath and revelation of the righteous judgment of God, 6 who will render to each person according to his deeds: 7 to those who by perseverance in doing good seek for glory and honor and immortality, eternal life; 8 but to those who are selfishly ambitious and do not obey the truth, but obey unrighteousness, wrath and indignation. 9 There will be tribulation and distress for every soul of man who does evil….
And Paul emphasizes that this is true for Jew and Gentile alike.
Chapter 3: We all sin under the Law, Jew and Gentile alike, but the Law does tell us what sin is and it remains valid. We — again, Jew and Gentile alike — are justified not by works under the Law but by the grace of God and faith in Christ (and “God presented [Christ] as a sacrifice of atonement,” 3:25).
Chapter 4: Paul explains how Abraham was made righteous by his faith, not by works or circumcision, the latter of which was only a sign of his righteousness. And Abraham is the father of us all. Paul sometimes appears to be trying to reassure the Jews that they are special while at the same time saying that the Jew-Gentile distinction no longer matters. But I think that what Paul is saying is that, sure, the Jews are/were special insofar as God spoke to them, but with Christ now God has saved all of us, making us all special in the way the Jews alone once were.
Chapter 5: Jesus’ death saved us all, just as through Adam’s sin we all became sinners. There’s also this famous passage in which Paul explains how our tribulations make us better (verses 3-5): “[W]e also exult in our tribulations, knowing that tribulation brings about perseverance; and perseverance, proven character; and proven character, hope; and hope does not disappoint, because the love of God has been poured out within our hearts through the Holy Spirit who was given to us.”
(At this point I would be remiss not to note that we are now in the middle of some heavy theological passages. Paul’s discussion of Original Sin is centered at 5:12-21, for example, and my NIV study Bible notes (emphasis on the original) that chapters 6-8 “deal[] with sanctification–the change God makes in our lives as we grow in faith. Chapter 6 explains that believers are free from sin’s control. Chapter 7 discusses the continuing struggle believers have with sin. Chapter 8 describes how we can have victory over sin.”)
Chapter 6: But we should still try to avoid sinning. “For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord” (verse 23).
Chapter 7: Paul continues his discussion of the Law, making in particular I think the interesting point that it can actually increase the amount of sin for some people simply by naming, describing, and prohibiting it (the forbidden fruit is sweeter, precisely because it’s forbidden). Paul laments that he doesn’t do what he knows he should do, and does instead what he knows he shouldn’t.
Chapter 8: Christ has set us free from the law of sin and death, and we can never be separated from Him, and we should live accordingly. Verse 31 is the famous, “If God be for us, who can be against us?” Note: Predestination and “the elect” are in verses 28-30, 33; I discuss predestination and works-versus-faith in other posts on this site, by the way.
Chapter 9: This chapter and the following two (i.e., chapters 10 and 11) focus on Israel. Paul is a Jew, after all, and remains emotionally and intellectually bound to his brethren. These three chapters wrap up the more theological part of Paul’s letter; in chapter 12 he then shifts to discussing how Christians ought to behave. Anyway, Paul begins chapter 9 in anguish: As a Jew, he is unhappy with his stubborn people. He recounts briefly some patriarchal history and concludes in anguish, too:
30 What shall we say then? That Gentiles, who did not pursue righteousness, attained righteousness, even the righteousness which is by faith; 31 but Israel, pursuing a law of righteousness, did not arrive at that law. 32 Why? Because they did not pursue it by faith, but as though it were by works. They stumbled over the stumbling stone ….
Chapter 10: More anguish about Paul’s fellow Jews. They must accept Christ to be saved, and many have not.
Chapter 11: But Jews can be saved, just as the Gentiles were saved. (A couple of notes: Paul mentions again “the elect” (verse 7), and calls himself “apostle to the Gentiles” (verse 13; see also 15:16).) As noted above, chapter 11 concludes the more theological part of Paul’s letter, and so it ends fittingly with a doxology (verses 33-36).
Chapters 12 and 13: As noted earlier, with chapter 12 Paul shifts from theology to discussing how Christians ought to behave; that will continue until the middle of chapter 15, when he starts signing off. Since I am particularly interested in collecting such passages, this is a treasure trove, and for chapters 12 and 13 in particular, it’s easiest to quote the whole chapter and indicate by ellipses what is not included. So here is chapter 12:
…. 2 [D]o not be conformed to this world, but be transformed by the renewing of your mind, so that you may prove what the will of God is, that which is good and acceptable and perfect.
3 For through the grace given to me I say to everyone among you not to think more highly of himself than he ought to think; but to think so as to have sound judgment, as God has allotted to each a measure of faith. 4 For just as we have many members in one body and all the members do not have the same function, 5 so we, who are many, are one body in Christ, and individually members one of another. 6 Since we have gifts that differ according to the grace given to us, each of us is to exercise them accordingly: if prophecy, according to the proportion of his faith; 7 if service, in his serving; or he who teaches, in his teaching; 8 or he who exhorts, in his exhortation; he who gives, with liberality; he who leads, with diligence; he who shows mercy, with cheerfulness.
9 Let love be without hypocrisy. Abhor what is evil; cling to what is good. 10 Be devoted to one another in brotherly love; give preference to one another in honor; 11 not lagging behind in diligence, fervent in spirit, serving the Lord; 12 rejoicing in hope, persevering in tribulation, devoted to prayer, 13 contributing to the needs of the saints, practicing hospitality.
14 Bless those who persecute you; bless and do not curse. 15 Rejoice with those who rejoice, and weep with those who weep. 16 Be of the same mind toward one another; do not be haughty in mind, but associate with the lowly. Do not be wise in your own estimation.17 Never pay back evil for evil to anyone. Respect what is right in the sight of all men. 18 If possible, so far as it depends on you, be at peace with all men. 19 Never take your own revenge, beloved, but leave room for the wrath of God, for it is written, “Vengeance is Mine, I will repay,” says the Lord. 20 “But if your enemy is hungry, feed him, and if he is thirsty, give him a drink; for in so doing you will heap burning coals on his head.” 21 Do not be overcome by evil, but overcome evil with good.
And here is chapter 13 (I have to say that the first paragraph (verses 1-7), on accepting governmental authority and even giving it a divine imprimatur, is eyebrow-raising for an American — it goes beyond just rendering unto Caesar what is Caesar’s on April 15 — and one would like to cabin it in some way to Paul’s specific audience and context; after all, Daniel in the Old Testament was willing to stand up to governmental authority, as were the early Christian martyrs, Paul himself included):
1Every person is to be in subjection to the governing authorities. For there is no authority except from God, and those which exist are established by God. 2 Therefore whoever resists authority has opposed the ordinance of God; and they who have opposed will receive condemnation upon themselves. 3 For rulers are not a cause of fear for good behavior, but for evil. Do you want to have no fear of authority? Do what is good and you will have praise from the same; 4 for it is a minister of God to you for good. But if you do what is evil, be afraid; for it does not bear the sword for nothing; for it is a minister of God, an avenger who brings wrath on the one who practices evil. 5 Therefore it is necessary to be in subjection, not only because of wrath, but also for conscience’ sake. 6 For because of this you also pay taxes, for rulers are servants of God, devoting themselves to this very thing. 7 Render to all what is due them: tax to whom tax is due; custom to whom custom; fear to whom fear; honor to whom honor.
8 Owe nothing to anyone except to love one another; for he who loves his neighbor has fulfilled the law. 9 For this, “You shall not commit adultery, You shall not murder, You shall not steal, You shall not covet,” and if there is any other commandment, it is summed up in this saying, “You shall love your neighbor as yourself.” 10 Love does no wrong to a neighbor; therefore love is the fulfillment of the law.
… 13 Let us behave properly as in the day, not in carousing and drunkenness, not in sexual promiscuity and sensuality, not in strife and jealousy. 14 But put on the Lord Jesus Christ, and make no provision for the flesh in regard to its lusts.
Chapter 14: It’s all on food, and boils down (so to speak) to this: There are no limits on what you can eat — that is, in particular, the “clean”/”unclean” boundary no longer exists — except that, if it would create a “stumbling block” to the faith of another believer if he saw you eating something, then you refrain from eating that. This is the same point Paul makes in I Corinthians (chapters 8 and 10), although there the problematic food is that which has been sacrificed to idols.
Chapter 15: Paul finishes up his rules for Christian living. “Now we who are strong ought to bear the weaknesses of those without strength and not just please ourselves. Let each of us please his neighbor for his good, to his edification” (verses 1-2). And “Wherefore, accept one another, just as Christ also accepted us to the glory of God” (verse 7). He concludes (verse 13) with a benediction: “Now may the God of hope fill you with all joy and peace in believing, that you may abound in hope by the power of the Holy Spirit.”
In the last part of chapter 15 (verses 14-33), Paul turns to his personal plans: his ministry to date, his going now to go to Jerusalem to deliver his collection for “the poor among the saints” there, and his hope — now that his work is finished in the East — to continue his evangelizing in Spain.
Chapter 16: This is almost all Paul sending his greetings and then passing along as well the greetings of others who are with him. But there’s also this:
17 Now I urge you, brethren, keep your eye on those who cause dissensions and hindrances contrary to the teaching which you learned, and turn away from them. 18 For such men are slaves, not of our Lord Christ but of their own appetites; and by their smooth and flattering speech they deceive the hearts of the unsuspecting. 19 For the report of your obedience has reached to all; therefore I am rejoicing over you, but I want you to be wise in what is good and innocent in what is evil. 20 The God of peace will soon crush Satan under your feet.