How Did the Earliest Church Define Salvation?

This question came up for me in a discussion of the meaning of "saved" in Acts 15:1. >But certain ones having come down from Judea were teaching the brothers, "Unless you are > circumcised according to the custom of Moses, you are not able to be > saved [σῴζω]." The questioner wanted to know the meaning of "saved" in that specific verse. What I'm interested in here is finding resources dealing with the how the earliest church thought about salvation generally. In other words, how did the church think about salvation before Paul wrote about it and before the Gospels were disseminated? Questions that come to mind include: did pre-Pauline Christians think of salvation as being related to eternal life per se? Or did they still think in traditional Jewish terms, such as Jesus being the one who would "restore the kingdom to Israel?" (Acts 1:6). Were some of them expecting Jesus to return in their lifetimes to liberate Israel from Roman rule, rather then thinking of him as a spiritual savior who would liberate them from death and sin, as Paul thought. I would appreciate references to scholarly works on this subject, including relevant quotes if possible.