He hardens them in the position they themselves choose to be in. Like Pharaoh.God says through Isaiah, blind them, them, so that they will not turn, and be healed. Jesus says, therefore they could not believe.
there's a purposeful action here with an intended result, which i found utterly astounding!! it's not just happenstance, like, yeah, some will probably harden, some will probably soften, let's see how it shakes out -- no, He intentionally hardens in order to exclude those under His judgement. God knows what He does, and He does all He intends.