Question. Why did God harden the hearts of the people in John 12? Was this fair to them?
John 12:37-41 But though he had done so many miracles before them, yet they believed not on him: That the saying of Esaias the prophet might be fulfilled, which he spake, Lord, who hath believed our report? and to whom hath the arm of the Lord been revealed? Therefore they could not believe, because that Esaias said again, He hath blinded their eyes, and hardened their heart; that they should not see with their eyes, nor understand with their heart, and be converted, and I should heal them. These things said Esaias, when he saw his glory, and spake of him.
It is not unusual for folks to think the hardening of hearts and blinding of eyes mentioned in John 12 seemed unfair. A lot of what we Americans perceive as "fairness" may not be based on the Bible as much as it is on our own conclusions. We should not predetermine what we want to believe about fairness and then look for it in the Bible. We must accept things as revealed in the Bible. Overall the Bible teaches that God does as He pleases -- including that He can determine what people think and do. It is hard to accept the Bible literally and not accept that fact.
In John 12 John is talking about God judging Israel as a nation as he sets them aside to work through the churches. Paul applies it that way (referring to the same passage in Isaiah 6:9-10) when talking to the Jews in Acts 28:24-29, and seems to also in Romans 11:7-8. Jamieson, Fausset and Brown Commentary puts it this way, which sums it up: "That this expresses a positive divine act, by which those who wilfully close their eyes and harden their hearts against the truth are judicially shut up in their unbelief and impenitence, is admitted by all candid critics..." and Matthew Henry writes, "Judicial blindness and hardness are in the word of God threatened against those who wilfully persist in wickedness, and were particularly foretold concerning the Jewish church and nation."
John Gill writes, "God had determined to leave them to the blindness and hardness of their hearts, and to deny them his grace, which only could cure them of it, and enable them to believe: he had foretold this in prophecy, and they were manifestly the persons spoken of; and therefore considering the decrees of God, the predictions of the prophet, and the hardness of their hearts, they were left unto, it was morally impossible they should believe,"
The revelation of the glory of the Lord in Jesus (notice verse 37, compared with verse 41) produced disbelief in these people (as a whole, not every individual; notice verses 11 & 42). It can be summed up this way. The Jews as a nation rejected Jesus (cf. John 1:11) and He as God had rejected them.