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.” (John 12:39-40 ESV)
One of the themes in John 12 concerns the rejection of Jesus. Most of the people in Jerusalem that Palm Sunday had seen or heard of the signs and miracles Jesus had performed, yet many of them doubted that He was the Messiah or even a prophet sent from God. This is why John cited Isaiah 6:9-10, the commission that the Lord gave that prophet when he saw the Lord in all His heavenly glory.
The message to the Jews of Isaiah’s day was one of coming judgment. They had refused to trust, serve and obey the Lord. Consequently He pronounced them to be blind and stubborn, hard of heart and worthy of judgment. Yet there was still hope for the people though they were going into exile: the Lord was not going to desert them.
John’s citation of Isaiah confirms that the Jews who rejected Jesus were rejecting God. The Lord hardened their hearts because of their attitude. The same is true today of those who reject Jesus. There will come a time when they will no longer be offered an opportunity to accept the gift of salvation He offers. Then the Lord will give them what they want: an existence without Him. This thought should sadden us so much that it ought to provoke us to present the gospel to our friends, family and neighbors before their hearts are closed. Who knows that the words we say or actions we perform in the name of Jesus will lead them away from eternal punishment into His loving arms.