This letter by Paul to the Christians in Rome is considered his masterpiece. It is partly a recruitment letter, he is hoping that many of the churches in Rome will support his mission to Spain. Being a recruitment letter, it is also a comprehensive theological treatise - he is outlining the content of what he will be teaching and preaching in the far West. Being a pastor, he also addresses social, ethical, and spiritual issues that are afflicting the Christians in Rome. Being a cosmopolitan empire capital, there is both extreme wealth amongst a few, and extreme poverty for too many; there is division between freemen and slaves, gender conflict, as well as ethnic tensions between Jews and Gentiles - as well as all sorts of other kinds of racism.
Paul's reputation precedes him - the same concerns, ideas, fears, and loves that people today have of Paul were likely felt back then. Thus he wants to make sure that even though he is coming hoping to receive money and prayers from them, he is also coming to give of himself, his skills, his wisdom, and his fiery love.
Verses 1-17 are his opening to the letter, he identifies himself, his source of authority, and addresses the people he is writing to. Verse 16-17 is a famous line: I am not ashamed of the gospel, because it is the power of God that brings salvation to everyone who believes.
Verse 18 begins the controversial elements of his letter - and it only heats up through the rest of the chapter. Paul needs to establish what we need salvation from, he needs to contrast God's righteousness with Humanity's unrighteousness, compare "living by faith" with "living under wrath".
Paul argues that people should know enough about God to seek him based on what they observe in nature and the world around him. But people have neglected or rejected this knowledge, and thus have shut themselves off from any other revelation/light by which to live. By turning away from God they open themselves up to a depraved way of life, a way of life that God then lets them walk into with undiluted consequences.
His example of sexual impurities is given to highlight how sad and destructive this way of life devoid of God becomes over time. Paul has a high view of sexuality (see Eph 5). He seems to be well aware of how beautiful and powerful sex can be when enjoyed in the light/revelation of God. But in darkness sex becomes an act of animal lust and overpowering by one over another. Some pscyhologists explain homosexuality and lesbianism as an sex addiction. Addictions can result from abuse or neglect. In a world turned away from God, people abuse one another with no divine restraints, and neglect becomes a black hole. This is some of the argument Paul seems to be making in this opening chapter.
It is a universal situation - all people in all places must deal with abuse and neglect, no matter how slight or blatant it may have been in their life. And all people have the potential to do many unrighteous things, even though they know better. They may even sin blatantly, even though they confess Jesus as their King.
Who can rescue you or me in a world of abuse and neglect, a world determined to justify existence apart from God? What sexual deviancy is your secret? What part of your sex life are you ashamed of, disappointed in, been abused or neglected?
Paul asserts that knowledge of God is the way to salvation. See Psalm 119.