First, we’ll set the foundation for exactly what “the gospel” is — as the Bible pronounces it as “of first importance,” we should do no less:
(I Corinthians 15:1-4) “Now I would remind you, brothers, of the gospel [Greek transliteration euangelion: good news, glad tidings] 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, that he was buried, that he was raised on the third day in accordance with the Scriptures.”
There are two sides of the gospel, the “good news” of the New Testament: an objective side and a subjective side. The objective content of the gospel is the person and work of Jesus — Who he is and what he accomplished in his life. The subjective side is the question of how the benefits of Christ’s work are appropriated to the believer. There, comes to the fore the doctrine of justification, or, how a person who has broken divine law gains a right standing before the judgment throne of God.
Many New Testament passages could be used to establish what the gospel is, but the following may serve as a summary:
The gospel is the surprising fulfillment of God’s work for the sake of saving the nations through Israel by sending his beloved Son, Jesus Christ, the Messiah, the Son of Man and the Son of God. In Christ, God was reconciling the world to himself. He proclaimed that the gospel was the kingdom of God at hand in him. Jesus, as the suffering servant, died as a ransom and propitiating sacrifice for humanity’s sins. His resurrection brings life out of death for all who place their faith in him. He fulfilled the covenantal requirements of Israel and makes the new covenant of God’s blessing and peace available to all who place their faith in his faithfulness. Through his ascension to heaven He made available the promise, the Holy Spirit, to empower his church for living a cross-shaped life of self-denial and grateful servitude. His gospel includes the promise of his return when he will bring justice, equity and the day when he will make all things new, establishing a new heaven and earth.
Or:
Jesus saves sinners to the glory of God.