Though He had done so many signs before them, they still did not believe in Him, so that the word spoken by the prophet Isaiah might be fulfilled: "Lord, who has believed what he heard from us, and to whom has the arm of the Lord been revealed?" Therefore they could not believe. For again Isaiah said, "He has blinded their eyes and hardened their heart, lest they see with their eyes, and understand with their heart, and turn, and I would heal them." Isaiah said these things because he saw His glory and spoke of Him. (John 12:37-41)If you're paying attention, this is a disturbing passage. We like to think that God hopes to save everyone and works toward that end and all that -- very warm and friendly stuff -- but this seems to say otherwise. This appears to say that there are those who cannot believe (John 12:39) -- actually lack the ability -- and the reason that they cannot believe is "He has blinded their eyes and hardened their heart, lest they see with their eyes, and understand with their heart, and turn, and I would heal them." (John 12:40) Notice that it doesn't say that they have blinded their eyes and hardened their heart. It doesn't even say that the god of this world has done it. It says "He", speaking of God, has done it.
Now, there are all sorts of twists and turns we can take here to try to alleviate this. Maybe it doesn't mean that He did it. Maybe it just means that He allowed it. They did it to themselves. Like Pharaoh who hardened his own heart until God accomplished it by merely letting him do it to himself. Maybe it means that God allowed Satan to do it. So maybe it doesn't require active participation on the part of God to make these people blind and deaf. What remains inescapable is that 1) He knew about it in advance and 2) allowed it to happen. He knew there would be some -- always will be some -- who cannot come to believe because they are spiritually blind and deaf.
So, go about whatever dance you want to make that work for you. Maybe you'd like to think that God is not capable of changing that. Not me, but maybe you would. Maybe you'd like to think that God prefers Human Free Will to His own, so He won't interfere. Again, that is not for me, but maybe it is for you. Maybe you're even fine with "God did it". But it remains inescapable that in some sense this was God's foreordained plan. He knew it or allowed it or caused it and did not change it.
My question for you, then, is not how or even why. My question for you is, if this was actually God's plan, is that okay with you? If God planned to have people who could not believe and repent and He either could not or did not do something to overcome that, does that meet with your approval?
You see the problem, don't you? On one hand it is entirely possible that we could end up disapproving of God's choices or capabilities or actions. On the other hand we're actually submitting God to our approval. As if we have any grounds to do so. Seems to me our only right response is, "Not my will, but Yours, O Lord." If your only response is the right one -- "Whatever You do is right, Father. Blessed be the Name of the Lord." -- then you're in the right place. If you're thinking that God has to pass inspection, then you're standing directly on the core of idolatry -- "I will be like the Most High."