"Gospels did not originate with Jesus and his followers. Rather they co-opted them...
"Gospels worked something like this:
"– a battle between two competing rulers would take place, and one would win a divisive victory
"– the victor would send out his heralds (official messengers) to the different territories of the empire declaring that so-and-so (Augustus, for instance) had won a great victory, and he was now the world’s new emperor.
"– the new emperor was described as 'Lord and Savior,' as well as 'Son of God,' and worshiped as God. Peace and prosperity were promised to come with the establishment of his rule.
"If you heard a gospel in that time, you had a decision to make. Would you believe the messengers? Would you pledge allegiance to this new ruler, or would you stay loyal to the old? If you came to the conclusion that they were in fact telling the truth, you would reorder your life as if the new emperor was already there, and his reign was already established in your locale. In this way, you were manifesting his rule. You would become a living preview of the new age this ruler was to bring."
https://web.archive.org/web/20180802043011/https://altarandthrone.com/do-we-actually-know-what-the-gospel-is/