This is a greeting, but it is more than just "hello."
Four ways that God works:
1. God works through grateful Christians. (v. 8)
Gratefulness is the gospel in action. An ungrateful Christian is an oxymoron.
2. God works through faithful local churches. (v. 8)
The church doesn't have to be unique or special. Jesus already is.
3. God works when people sacrifice for one another. (v. 11)
Paul isn't just concerned about helping them, but also being helped by them. If we ONLY serve where we are gifted, we lose out on mutual benefit. We don't need official church "ministries" to do this - giving your life away IS ministry.
The church is not made up of ministries; it is made up of people. Who can you pray for and serve?
4. God works through the consistent preaching of the gospel. (v. 15)
They are already Christians. But Paul still wants to preach the gospel to them. Why? Because they still need to hear it.
We forget what we know. And sometimes we doubt what we know. We need a regular reminder that our sins have been punished on the cross. We have been forgiven. And because of the resurrection, the power of sin is defeated now. We are declared righteous. Because of Jesus, we are righteous before God. Righteous behavior is the result, not the cause.
Verses 15-17 is the main point of the book of Romans - the rest is commentary on those verses.