The gospel, while clear, can be hard to verbalize. It’s not because it hasn’t been perfectly laid out in Scripture or that it doesn’t have a defined content, but more due to the richness and depth and wonder and magnificence of it all. If you were to ask 10 people what the gospel is, you’d almost certainly get 10 answers that are each distinct in some way. It is a dynamic message that has so many implications and reveals so much about God and his plan for all creation. And while it can be helpful to crystallize it into something like, “Jesus saves sinners” it’s just as true that the gospel speaks to how “God sanctifies saints.” Words like cross, sin, substitution, penalty, hell, heaven, faith, believe, redemption, reconciliation, peace, wrath, sanctification, Adam, Jesus, resurrection, justification, adoption, salvation, union with Christ, freedom, victory and a whole host of other terms come to mind when we talk about the gospel. Paul summarizes the gospel in this way: “..that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures…” (1 Cor 15:4). And I’d suggest that Paul, who magnificently lays out God’s plan of redemption in the first 11 chapters of Romans, best captures the glory and awe of the gospel at the end of chapter 11, “Oh the depth of the riches and wisdom and knowledge of God! How unsearchable are his judgments and how inscrutable his ways!” It’s a fitting exclamation point to what he has been telling the Romans up to that point. We too must continue to bask in the richness of the gospel over and over, seeking to understand the depths and richness of this good news more and more and become just as drop-jaw amazed as Paul was.
Trevin Wax has compiled a rather large list of gospel definitions given by various theologians, pastors, and Christian organizations. You can find it here: http://thegospelcoalition.org/blogs/trevinwax/2009/09/14/gospel-definitions-2/