What is the Gospel?

The title of this book is the question which was posed to a number of pastors who come under the banner Reformed. The reason for this question being asked was to discover and then examine what exactly men of high renown who lead people every Sunday to worship and who are trusted by hundreds perhaps thousands of people actually say the Gospel is. What do they say must be believed in order for one to be saved and what do they say it is that if one does not believe it one evidences a lost state regardless or how religiously zealous and morally upright one may be? Are they true Gospel preachers leading their flocks on the narrow way or are they in fact blind leaders who are themselves deluded by and promote a false gospel which does not save but rather draws its listeners and believers onto the broad way that leads to destruction?