Let me begin by saying I love what Frame and Storms have written. I would simply add that the gospel is also the good news that I have been rescued from Satan- the enemy of my soul, and that Jesus is establishing his kingdom.
What makes all of this so wonderful and perpetually relevant for the people of God is that in all of this, the gospel reveals something of the worth, beauty, splendor and glory of Jesus. Through the gospel, there is the perpetual revelation of the glory of God in the face of Jesus through the gospel, and this revelation is one that touches my mind and heart so that I know that I know….that I know God as the Spirit bears witness with my spirit.
As we continue to answer what “is” the gospel, I would say that it “is” the centerpiece of discipleship. Paul exhorted Peter that he was failing to “live in line with the gospel.” At the heart of all discipleship is the gospel. By that I mean that we encourage one another to live out its implications, to believe and remember its truths forward, and to see the finished work of Jesus come to bear in our lives.
The gospel is also the power of God. It is the only power on earth, in the universe for that matter that has the power to take the most broken aspects of our lives, families and society and to redeem them at such a profound level that they bring glory to God (radical, dynamic authentic change). The power that spoke light into darkness and water to wine also breaks the hardest hearts and progressively turns people into the image of Christ as the same God speaks through the gospel.
The gospel is also the message and strategy for mission. The gospel is what the nations need! Nothing else has the power to sustain a people in persecution, to build the church, and to captivate the hearts of the lost. It is the gospel that is going out to all the earth bearing fruit and not returning void. While we are called to meet the most basic needs of people (feeding, shelter, relationship, etc) we do so while we also seek to meet their most fundamental need, to be reconciled to God the Father.
Finally, the gospel is the way I read and understand scripture. If I am reading Moses or if I am reading Paul, I am looking for something that shows me the glory of Jesus in the gospel.