Romans 1:1-4 - All about Jesus
The way Paul serves Jesus is as an apostle, which means he's someone whose gift is to make disciples and plant churches in places where there are none. Jesus told Paul to do this job and Paul is doing as he's told because he lives to serve Jesus.
Paul then mentions three things about Jesus...
First, he reminds the Christians in Rome that Jesus came to fulfill ancient prophecy. Throughout the Old Testament there are hundreds of prophecies predicting the arrival of the 'messiah' - God's chosen rescuer. Jesus fulfills them all because they were all about him! God knows and plans the future, told the prophets in advance and kept his promises to come and rescue his people!
Second, Paul says that Jesus was a real human man from the family line of David, just as the prophets promised. Jesus was fully human. He cried, got tired, got hungry and thirsty and felt pain like anyone else would. Being genuinely human means that Jesus could live a life like we do but without sin and properly represent human beings when he died in our place for our sin on the cross.
Third, Paul explains that Jesus was not just a man but was the 'God-man'. Jesus wasn't a man who became God but God who became a man. Jesus is 'Immanuel', which means 'God with us.' And Paul is saying that the resurrection of Jesus from the dead proves that this is true. How else would it happen? Unless Jesus was fully God, he would not have lived a sinless life and his death on the cross would not have been anything special, let alone payment for the sin of the whole human race.
Paul starts as he means to go on. He's all about Jesus and he wants to teach us more about this man who is God - Jesus Christ 'our Lord'.