No one knew the Messiah was coming to die for their sins, even though it was written down.
You may as well face the facts.
I don't do STP on 'hidden in plain sight' when referring to the OT. He's about as confused as it gets.
The whole problem starts with a movement that says the Bible is a confusing mess that 'needs' their fix. That's what stands behind the literal readers that defy so much of the NT. That created an RT so they'd have more support because now, man, they really had a clear enemy.
It is actually amusing that STP would use that expression because it means the opposite of what he believes about the NT, or else we have no actual disagreement. I do not find D'ists able to avoid their love for disagreement; their identity is wrapped up in disagreeing.
The Gospel is hidden in plain sight in the OT. That is what Rom 1 and 16 and 2 Cor 5 say. Paul's 'revealed to me' did not mean it was not there, Eph 3 on that. It means it was hidden to how intertestament, post-exile Judaism moved. Most of the NT is written in conflict with IT,P-E Judaism.