Alright, so... If I were to ask (the EO, that's why I'm asking here) what is the Gospel? What would your answer be?
There's a book called "
Arise O' God" by Fr. Stephen Andrew Damick that goes exactly into this from the ancient context.
Essentially, Ευαγγέλιον or "Gospel" was a genre of ancient writing. Sort of how we have non-fiction, biographies, fantansy, horror, instructionals, etc. today if you were to look in a book store, there's different genres. Evangelion were a genre in that respect. What were Evangelion? That's the question.
So, the ancient world was very....tumultuous. Wars everywhere. Kingdoms, tribes, empires conquering each other
all the time. So, let's just use Caesar Augustus as an example of a conquering king. Let's say you lived in a Greek town called....Corinth. (History nerds, pls don't crucify me) So, Augustus is conquering Greece to expand the Roman Empire, and he wins a battle that leaves it wide open for him to march into Corinth and take over. Augustus would send out (Apostle means the being 'sent out') a herald to announce to Corinth that
"Caesar Augustus, the son of god, has just won the battle against your overlords and will be arriving to uphold peace in Corinth for a thousand years, and you can either receive his lordship over you or be removed and killed outside of the town."
The townsfolk would either accept Augustus as the new lord over them or not. That's roughly what Ευαγγέλιον was as a genre. A proclamation of victory and lordship and instructions on how to be integrated into the new lord's realm.
So, that's what the Apostles did, they went into towns to declare Christ's victory over the enemy (death). This is why in the book of Acts, whenever the Gospel was proclaimed by the Apostles, the people ask "What must we do to be saved?" The Apostles would then give them instructions on how to be saved:
"Repent, be baptized, receive the gift of the Holy Spirit." If you read throughout the book of Acts, you will notice that whenever the question is asked: "What must I do to be saved?" the answer is always the same:
"Repent, be baptized, receive the Holy Spirit. You and your whole family." It's a recurring pattern starting from Acts 2:37-38 and throughout the book.
Now, we can go into the whole ancient meaning of 'repent' (μετανιώνω) and receiving the Holy Spirit, but that's a question for another time.