According to Paul, the gospel is all about Jesus. He mentions its contents here: ‘concerning his Son, who was descended from David according to the flesh and was declared to be the Son of God in power according to the Spirit of holiness by his resurrection from the dead, Jesus Christ our Lord.’ As we read that summary, we can identify several crucial aspects of the person and work of Christ.
First, Jesus is both God and man. His deity is seen in the statement that he is God's Son and his humanity is seen in the statement that he is the Son of David. His deity had no beginning and his humanity will have no end. In the union of the divine and human natures of Jesus we see a great miracle, one before which we should bow with wonder. What would have seemed impossible was achieved when the human nature of the Son of God was conceived in the womb of Mary. Although it may seem complicated, the gospel is not explained unless the reality of his deity and humanity is stressed.
Second, the gospel includes what happened to Jesus at his resurrection and afterwards. Paul says several things about what happened to Jesus at that time. It is important to see that what Paul says about Jesus here is connected to him being the promised Son of David is, that is the Messiah. His resurrection declared him to be what probably was not seen so clearly before. The Old Testament predicted a Messiah who would have universal power. Before his death, there is no suggestion that Jesus wanted to be a political Messiah who would deliver the Romans. No, his path to universal sovereignty included his death and resurrection, followed by his ascension and enthronement, when he was recognised as Lord. The gospel includes an explanation of his sufferings and glory.
How was the resurrection brought about? Paul says it was through the Spirit of holiness. Some discussion has taken place over what he meant. Did he mean that the Holy Spirit raised Jesus from the dead or did he mean that Jesus was raised from the dead because he was holy and death could not hold him? We might say that both teachings are true, but only one of them can be the truth mentioned here. I suspect it is a reference to the work of the Spirit when raising Jesus from the dead.
There is a sense that what Paul is stressing here is what the Father did in the work of salvation. After all, it was the Father who provided the Son with his human nature (the Son assumed it into union with himself and the Spirit conceived it in the womb of Mary) and it was the Father who raised Jesus from the dead and exalted him to the highest place (as Paul says in Philippians).
Of course, there is a lot more to the gospel that the details we have just mentioned, but it is good for us to think about how each person of the Trinity contributed to our salvation. And the verse that is best known for highlighting the work of the Father in this regard is John 3:16.