Paul offers us a near-summary of the gospel in poetic terms in 2 Timothy 2:

8 Remember Jesus Christ, raised from the dead, descended from David. This is my gospel, 9 for which I am suffering even to the point of being chained like a criminal. But God’s word is not chained. 10 Therefore
I endure everything for the sake of the elect, that they too may obtain
the salvation that is in Christ Jesus, with eternal glory.

11 Here is a trustworthy saying:

 If we died with him, we will also live with him;
12 if we endure, we will also reign with him.
If we disown him, he will also disown us;
13 if we are faithless, he will remain faithful, for he cannot disown himself.

Here is a fact: there is not enough resurrection in gospel preaching. Gospel preaching too often gravitates to sin as guilt and the cross as the only gospel day event. But Paul summarizes his gospel here as resurrection and Davidic descent. I’ve never heard a gospel message that gets to the resurrection except in terms of going to heaven when we die and I can confidently say I have not heard anyone speak of Davidic descent — which means Jesus is Messiah, the long-awaited and promised Messiah.

The resurrection message, as the poetic lines make clear above, entail the death and dying with Christ. The gospel response then is to die with Christ and to rise with Christ. It is to embrace the dead-and-raised Messiah.

This completes the references in Paul to “gospel.”