● first literally understood as good news (concerning salvation?),
● second, after a fair amount of development, the story of the deeds of Jesus, and
● third, a written account of the relevant moments in Jesus' life.
Paul was at phase #1 in his use of "gospel".
A little later I said here,
With regard to εκκλησια (usually translated as "church" in a christian context), Jewish people were using it as a word to describe their cultic meetings. (See Sirach 15:5, 23:24 et al., and Philo De Virt. 108 & Special Laws 1.324f. Herod called a public meeting in AJ 16.62, 393.) So εκκλησια started its known life as a term for "meeting"/"assembly", a temporary coming together of people for some communicative purpose. I can add that "synagogue" similarly meant a gathering of people. It would be highly important to know when these terms developed into referring to more formal or established practices as a specific group sharing a specific cultic purpose and later again an architectural structure to house that activity. When did εκκλησια become a strictly christian notion for christians and "synagogue" for Jews?
The term "kerygma" eventually derived from κερυξ, "a herald", is a term for the central cultic message of christianity, that which christians preach. It has undergone an evolution in christian thought to go from the message of the herald to the message of christian faith.
(I could briefly mention the term "christ", which originally meant "ointment"/"what is spread on" etc. As a loan translation from Hebrew it gained the meaning "messiah" in Jewish Greek cultic contexts. But it already had cultic use for Paul to continue in his religious efforts.)
Such terms didn't come into existence when the Jesus bang happened. They had to be shaped into the usage we have inherited. This should indicate that we cannot assume to know the significance of such terms as they are used in the earliest christian literature based purely on what they have come to mean.
This may be an old idea. I don't know. But I haven't seen it mentioned anywhere. If you know of such a discussion I'd really like to know about it. Otherwise it would be worthwhile determining which words have been appropriated by christianity, what those words meant before christianity, and how they were used in the earliest christian literature.
At the moment I'm thinking about ευχαριστεω ("to bestow a favor on"/"to be thankful") and related words that give us "eucharist", the sacred meal, apparently derived from the fact that during the last supper Jesus gave thanks over the bread and the cup. What other christian cultic words come to mind, words appropriated from ordinary language to bear special meaning? Any ideas?
Could christian cultic language have hit the ground, running, with a vocabulary already adapted? That possibility seems highly improbable to me. If I'm correct, we should stop using meanings that don't reflect the earliest language usage. We might get closer to understanding the writers better.