Rahab was an instrument of God's plan. She had a plan because she was one of God's elect. And if it weren't for God's power, the Gibeonites would have folded like a cheap accordion.
Rahab was provided infallible witness. So was everyone else.
Rahab feared. So did everyone else.
Rahab knew. So did everyone else.
But both Rahab and the Gibeonites made informed, rational, deliberate willful decisions,
PUT THEIR LIVES ON THE LINE AND
CHOSE TO ENTER INTO THE COVENANT.
===========================================
What of Chorazin and Bethsaida? They made informed, rational deliberate willful choices just the same.