One must distinguish between, on the one hand, the gospel as what God has done ... and, on the other, what is demanded by God or effected by the gospel in assorted human responses.
...The gospel is what God has done, supremely in Christ, and especially focused on his cross and resurrection...
By contrast, the first two greatest commands—to love God with heart and soul and mind and strength, and our neighbor as ourselves — do not constitute the gospel, or any part of it. We may well argue that when the gospel is faithfully declared and rightly received, it will result in human beings more closely aligned to these two commands. But they are not the gospel.
Similarly, the gospel is not receiving Christ or believing in him, or being converted, or joining a church; it is not the practice of discipleship. Once again, the gospel faithfully declared and rightly received will result in people receiving Christ, believing in Christ, being converted, and joining a local church; but such steps are not the gospel. The Bible can exhort those who trust the living God to be concerned with issues of social justice (Isa 2; Amos); it can tell new covenant believers to do good to all human beings, especially to those of the household of faith (Gal 6);
... We may even argue that some such list of moral commitments is a necessary consequence of the gospel. But it is not the gospel. We may preach through the list, reminding people that the Bible is concerned to tell us not only what to believe but how to live. But we may not preach through that list and claim it encapsulates the gospel...
Failure to distinguish between the gospel and all the effects of the gospel tends, on the long haul, to replace the good news as to what God has done with a moralism that is finally without the power and the glory of Christ crucified, resurrected, ascended, and reigning.