God only chose to reveal himself as Yahweh to only one region. Why I wonder, is it so that in different regions god seems to be completely different? curious.
He had to work with a specific people and within history. All due respect to Papist, but his answer is rather flippant and not in line with even what the RCC would teach. Read St. Paul, especially when he witnesses in Athens to them about their worship. Read what he says. Then read other writings of St. Paul (see the thread by PoorNick on The Law).
No doubt, it seems scandalous. And your questions are tough and realistic ones. If you decide, to read the Hebrew Scriptures with all the genocide, rape, incest, murder, adultery, etc., what I find so remarkable is the honesty of struggle that Israel maintained in their writings. Why keep all those scandalous stories about the Patriarchs and so on in your Holy Scriptures?
Read the Psalms, ain't all just Hallelujah.
And to answer your question more specifically and again in light of what I wrote above: God didn't zap anyone into the Truth. He had work with people who were willing (and most weren't and those who ended up working with God did so with much cajoling).
But to say the all the rest of creation was completely in the "dark" is not Biblical nor Christian.
Knowing the Truth ain't no walk in the park or desert as it were.
The recent Gospel reading on Sunday was the parable of the Last Judgement. Want to know the Truth? Be careful what you ask for, for to the degree we know the Truth and fail to LIVE it is to the degree of own condemnation.