While each Epistle has several purposes, there is often a main purpose that strikes the reader. Galatians was intended to address issues around Gentiles being part of the Church; 2 Thessalonians addresses eschatological doctrine; 1 Corinthians addresses chaos, morality, and discipline in church conduct and governance. We could say that the predominant purpose of Romans is to preach the Gospel and hand it on for posterity.
Romans is a long epistle and the Gospel portion of it is lengthy. This may seem odd to modern Christians who may be used to condensed versions of the Gospel along the lines of “Jesus died in our place so that our sins could be forgiven.” I hasten to add that I am not opposed to shortened versions of the Gospel where appropriate, but do point out that frequently in Acts the Gospel is preached in a narrative format, just as Paul chooses to in Romans.
Paul’s Gospel is international and rooted in the Jewish Scriptures, which he presents as a record of oracles, covenants, and promises made by God to His people Israel. Paul depicts Christ as Jewish and human, thus both particular and universal. He also presents Him as man and God: both perfect and able to identify with us in our plight. Paul’s Jesus is the Saviour, the One who fulfils God’s promises to Israel and delivers us from darkness and the wrath of God.
Paul makes clear from the beginning that this salvation is a gift from God, not merited by our works and to be received by coming to God and trusting Him, forsaking former religious ties, and holding on for the end, though we do not see God with our eyes in this life.
Paul tells the story of our descent into darkness, which simultaneously reveals both our need for salvation and the fate of those who will not repent. He illustrates our spiritual darkness with examples, ranging from polytheism and idolatry, which would have been familiar to the Roman’s, littered and Rome was with temples and statues, to sexual misconduct and general disobedience and selfishness.
Here Paul’s theology moves on to two points: God’s temporary abandonment of the Gentiles (Deuteronomy 32 and Psalm 82); and the fact that God does not force salvation on anyone: we must freely accept the Gospel.
This allows Paul to set up the election and purpose of Israel, which is an essential element of his Gospel narrative. Paul also begins warning that sin leads to death: there is something from which we are to be saved as well as Someone we are to be saved for.
All Along the Watchtower 
Nicholas, very good to see that you’re thinking of doing something on Romans. I came across some notes (basically I found one very good source). I’ll share with you the beginning of them.
The opening verses contain the kernel of the message that Paul is about to proclaim. His whole system of divinity is suggested in these verses and lines of extension can be carried from them to other parts of the letter where the subjects are dealt with in greater detail. For example, ‘promised beforehand through his prophets’ is taken up again in 3v21, 4v1-25.
In the first verse, Paul’s apostolic credentials are summed up. Even the word Paul has significance; previously he was Saul of Tarsus, but something decisive happened to him. He became a changed man and the change wrought within him gave him the right to preach the gospel to others, because it had first been good news to him. He could therefore confidently assert that the gospel was the power of God for salvation (1v16), because it had proved to be so in his own heart and life. The term ‘servant’ has a double meaning. On the one hand, it has the force of ‘bond-slave’, but it is also the term used to describe Moses in the Septuagint and therefore, at the same time, indicates an exalted position. In using this word, Paul simultaneously recognises that he is not his own and that he in the position of a ‘bond-slave’ before God; paradoxically, through being true to his calling, he is also exalted by God.
His position as bond-slave is the seed of the theme that he develops in chapters 6 – 8. It expresses his sense of being under an obligation to Christ that he can never fully discharge and therefore Christ’s bidding is the only possible concern in his life.
Paul is a ‘called apostle’. The believers at Rome in verse 7 are also described as ‘called’ and in both cases it is God who calls. The call has not only been given, but has also been obeyed. A Christian is one who has been called by God and who has obeyed the calling by believing in Christ. An ‘apostle’ is, literally, ‘a sent one’. In the strict sense, the word is used properly only of the Twelve, in the first instance, then of some others; for example, Barnabas (Acts 14v4), Andronicus and Junia (Romans
16v7) and of Paul himself. But in a more general sense, every Christian is ‘sent’, in the sense that every Christian is committed to be a witness and messenger of the gospel to others. The term ‘separated’, ‘set apart’, ‘reserved for the use of’ is also used in Acts 13v2 when the Holy Spirit said, ‘Set apart for me Barnabas and Saul for the work to which I have called them’, and in Galatians 1v15, where Paul speaks of God ‘who had set me apart before I was born.’ Separation is God’s act and the practical effect on the apostle is well summed up in the words `But only one thing I do: Forgetting what is behind and straining towards what is ahead, I press on towards the goal to win the prize for which God has called me heavenwards in Christ Jesus.’ (Philippians 3v13,14)
The picture is of a man claimed by God and utterly given to God for the gospel.
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