No other gospel

“I am astonished that you are so quickly deserting the one who called you to live in the grace of Christ and are turning to a different gospel— which is really no gospel at all. Evidently some people are throwing you into confusion and are trying to pervert the gospel of Christ. But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let them be under God’s curse! As we have already said, so now I say again: If anybody is preaching to you a gospel other than what you accepted, let them be under God’s curse!” (Gal. 1:6-9 NIV)

The gospel is “Christ died for our sins”

“Now I would remind you, brothers, of the gospel I preached to you, which you received, in which you stand, and by which you are being saved, if you hold fast to the word I preached to you—unless you believed in vain. For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures...” (1 Cor. 15:1-5 ESV)

The gospel is the power of God for salvation  

“For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek.” (Rom. 1:16 ESV)

Proclaim it to the whole creation

“And he said to them, “Go into all the world and proclaim the gospel to the whole creation.” (Mark 16:15 ESV)