Nathanael said to [Jesus], “How do You know me?” Jesus answered him, “Before Philip called you, when you were under the fig tree, I saw you.” Nathanael said to Him, “Rabbi, You are the Son of God! You are the King of Israel!” (John 1:48-49)
In John’s Gospel, life is first mentioned in 1:4, but the author doesn’t really unpack what he means by it until chapter 3. Meanwhile, John the Baptizer introduces Jesus as the one who “was before me” (1:15) and therefore as the Word (1:14), “the Lamb of God who takes away the sin of the world” (1:29), the one who baptizes with the Holy Spirit (1:33), the Son of God (1:34); Andrew introduces Him as the Messiah/Christ (1:41), as does Philip (1:45), and Nathaniel recognizes Him as Son of God and King of Israel (1:49) — which Jesus describes as Nathaniel believing (1:50). Following the first sign, the disciples believe in Him (2:11), and following His signs in Jerusalem, many “believed in His name” (2:23).
There’s no mention thus far of eternal life, but we have a small army of converts who believe in Him. Zane Hodges once pointed out that there’s a point where Peter clearly does believe that Jesus is the source of eternal life (Jn. 6:68) and clearly does not believe in the death, burial, and resurrection (Mt. 16:21-23), and yet we all think he’s saved nonetheless. Zane argued that established the primacy of the promise of life over Of course it would be much harder to make that same mistake today, but apply the same logic: all kinds of mistakes are still possible.
From one angle of view, searching for the right proposition, it would seem that they believed a splatter pattern of related things. From another perspective, they’re all focused on the same thing: Jesus. The propositions are there, sure, but you will ransack the Scriptures in vain trying to nail down The Saving Proposition with any kind of biblical authority, because it doesn’t exist. No passage of Scripture even poses the question, still less answers it. Different evangelistic encounters in Scripture employ different propositions. There’s one Person; many propositions that point out the Person in question. I could fairly say “The one who died for us and rose again” — that’s a totally reasonable answer, and the one Paul employs in 1 Cor. 15, but it doesn’t capture what Peter believed (Mt. 16:22), does it? We could say “The one who’s the Son of God” which captures what the man born blind believed in John 9, but the woman of Sychar in John 4 doesn’t seem to know anything of that. We could say “He’s the promised Messiah,” which is what she believed, but the man in John 9 doesn’t seem to be aware of it.
My claim is simple: what matters is that they’re all looking to the right Person, and what matters today is that we direct people to the right Person. The task is simple: start from where they are; point them to Jesus; share as much of Him as you can.
Full Contact Christianity 
It’s what I would call, “The Gospel in 3D”