For my part, I've studied NT Greek for about thirty years. I find the NT itself is most helpful, but I also compare notes and usage from the classics through the papyrii and the Greek Christian writers.
I don't believe the Gospel was ever lost. Perhaps you're thinking of Mormons and Jehovah's Witnesses. I believe it was always right there, on the surface of the pages of the Bible.
And as far as all this chatter about 1800 years later and all... maybe you're thinking of the various Ortho's or Roman Catholics. They're great believers in (=insisters on) playing "telephone" with the Bible.
Not Christians, though. We don't rely on men writing 1800 years later, or 1500 years later... or 1000, or 500, or even 100 years later.
We rely directly on God's Word itself. Drives cultists and the otherwise enslaved absolutely nuts (as predicted; Galatians 4:29), but that's what being a Christian is: standing faithfully on the Word of God Himself. It'll steer you straight TO Christ, and PAST silly (at best) diversions like trying to chat up dead people, and all -- to say nothing of the time and energy that goes into trying to spin and "defend" the silly practices.
I cannot recommend it to you too highly.
Dan
"Now people look at Orthodox and think it is just one more denomination," Schaeffer said. "But I look at it as unbroken continuity
From the laying of hands from the Apostles to their chosen bishops to the New Testament - unbroken continuity.