Trying to answer the question 'what is the gospel?', it may be useful to first set down what the gospel is not. But before that, a brief acknowledgement that what the gospel is involves some diversity of expression (as we will see in future posts). Then, a possibly helpful analogy to get us going.
Take the concept of 'health'. Some diversity of expression of 'health' is reasonable. Here in Aotearoa New Zealand, for instance, we have found it useful to understand 'health' for Maori and 'health' for Pakeha (European-background Kiwis) in different ways with consequences for different approaches to diagnosis and treatment. To give a one example, the communal aspect of Maori culture means that the presence of whanau (extended family) with a patient in hospital, to the extent of several people sleeping near the patient each night, can be vital to recovery. But these differences should not obscure the fact that a cancer growing inside a Maori body is the same as a cancer growing inside a Pakeha body, and if radiotherapy will treat the cancer in one, it will treat it in the other. So some difference of expression of 'health' between Maori and Pakeha is reasonable, but what is not reasonable is to say that one with cancer is 'healthy' and one without cancer is 'healthy'. What 'health' is not is that health means one thing to one person and another thing to another.
So, to what the gospel is not. Briefly, and without citation and argument. I hope things are fairly obvious here!
The gospel is not:
(1) One thing for one people group, or one era in history, and another for a different group or era.
(2) A message for some (those disposed to live by it) but not for others (those disinterested in it). Another way of putting this: the gospel is not the charter or constitution of a hobby group or club called 'church'.
(3) A human proposal up for debate because, like all human proposals it has flaws, needs revising for the needs of the day, etc.