Euangelion means good news — from eu (good) and angelia (message). In the ancient world it was the word for a herald's announcement of a great event: a military victory, or the birth or accession of a king. The New Testament seizes it to announce the greatest news of all — that in Jesus Christ, God has acted to save the world. Our English word gospel (from Old English god-spell, good story) translates it, and evangelist and evangelism come straight from it.
The gospel is therefore news before it is advice — a report of what God has done, not a list of what we must do. Paul summarises it: Christ died for our sins... was buried, and... rose again the third day. It is, he says, the power of God unto salvation to every one that believeth — a message so good that those who hear it cannot help but pass it on.
Euangelion in Scripture
For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek.