The gospel is not just a sequence of steps (say, the "Four Laws" of Campus Crusade or the "Six Biblical Truths" of Quest for Joy ). Those are essential. But what makes the gospel "good news" is that it connects a person with the "unsearchable riches of Christ."
There is nothing in itself that makes "forgiveness of sins" good news. Whether being forgiven is good news depends on what it leads to. You could walk out of a courtroom innocent of a crime and get killed on the street. Forgiveness may or may not lead to joy. Even escaping hell is not in itself the good news we long for - not if we find heaven to be massively boring.
Nor is justification in itself good news. Where does it lead? That is the question. Whether justification will be good news, depends on the award we receive because of our imputed righteousness. What do we receive because we are counted righteous in Christ? The answer is fellowship with Jesus.
Forgiveness of sins and justification are good news because they remove obstacles to the only lasting, all-satisfying source of joy: Jesus Christ. Jesus Christ is not merely the means of our rescue from damnation; he is the goal of our salvation. If he is not satisfying to be with, there is no salvation. He is not merely the rope that pulls us from the threatening waves; he is the solid beach under our feet, and the air in our lungs, and the beat of our heart, and the warm sun on our skin, and the song in our ears, and the arms of our beloved.
This is why the New Testament often defines the gospel as, simply, Christ. The gospel is the "gospel of Christ" (Romans 15:19; 1 Corinthians 9:12; 2 Corinthians 2:12; 9:13; 10:14; Galatians 1:7; Philippians 1:27; etc.). Or, more specifically, the gospel is "the gospel of the glory of Christ" (2 Corinthians 4:4). And even more wonderfully, perhaps, Paul says that the preaching of the gospel is the preaching of "the unsearchable riches of Christ" (Ephesians 3:8).
Therefore to believe the gospel is not only to accept the awesome truths that 1) God is holy, 2) we are hopeless sinners, 3) Christ died and rose again for sinners, and 4) this great salvation is enjoyed by faith in Christ-but believing the gospel is also to treasure Jesus Christ as your unsearchable riches. What makes the gospel Gospel is that it brings a person into the everlasting and ever-increasing joy of Jesus Christ.
The words Jesus will speak when we come to heaven are: "Enter into the joy of your Master" (Matthew 25:21). The prayer he prayed for us ended on this note: "Father, I desire that they also, whom you have given me, may be with me where I am, to see my glory" (John 17:24). The glory he wants us to see is the "unsearchable riches of Christ." It is "the immeasurable riches of [God's] grace in kindness toward us in Christ Jesus" (Ephesians 2:7).
The superlatives "unsearchable" and "immeasurable" mean that there will be no end to our discovery and enjoyment. There will be no boredom. Every day will bring forth new and stunning things about Christ which will cause yesterday's wonder to be seen in new light, so that not only will there be new sights of glory everyday, but the accumulated glory will become more glorious with every new revelation.
The gospel is the good news that the everlasting and ever-increasing joy of the never-boring, ever-satisfying Christ is ours freely and eternally by faith in the sin-forgiving death and hope-giving resurrection of Jesus Christ.
May God give you "strength to comprehend with all the saints what is the breadth and length and height and depth, and to know the love of Christ that surpasses knowledge" (Ephesians 3:18-19).
From Desiring God
an article by John Piper