I love this passage from J.I. Packer, one of my favorite writers, about the true gospel and its purpose. This is from A Quest for Godliness: The Puritan Vision of the Christian Life. He writes:
There is no doubt that evangelicalism today is in a state of perplexity and unsettlement. In such matters as the practice of evangelism, the teaching of holiness, the building up of local church life, the pastor’s dealing with souls and the exercise of discipline, there is evidence of widespread dissatisfaction with things as they are and of equally widespread uncertainty as to the road ahead. This is a complex phenomenon, to which many factors have contributed; but, if we go to the root of the matter, we shall find that these perplexities are all ultimately due to our having lost our grip on the biblical gospel. Without realizing it, we have during the past century bartered that gospel for a substitute product which, though it looks similar enough in points of detail, is as a whole a decidedly different thing. Hence our troubles; for the substitute product does not answer the ends for which the authentic gospel has in past days proved itself so mighty. Why?
We would suggest that the reason lies in its own character and content. It fails to make men God-centered in their thoughts and God-fearing in their hearts because this is not primarily what it is trying to do. One way of stating the difference between it and the old gospel is to say that it is too exclusively concerned to be ‘helpful’ to man—to bring peace, comfort, happiness, satisfaction—and too little concerned to glorify God. The old gospel was ‘helpful’, too—more so, indeed, than is the new—but (so to speak) incidentally, for its first concern was always to give glory to God. It was always and essentially a proclamation of divine sovereignty in mercy and judgement, a summons to bow down and worship the mighty Lord on whom man depends for all good, both in nature and in grace. Its centre of reference was unambiguously God. But in the new gospel the centre of reference is man. This is just to say that the old gospel was religious in a way that the new gospel is not. Whereas the chief aim of the old was to teach people to worship God, the concern of the new seems limited to making them feel better. The subject of the old gospel was God and his ways with men; the subject of the new is man and the help God gives him. There is a world of difference. The whole perspective and emphasis of gospel preaching has changed.