After describing the signs Jesus performed, John turns to Isaiah to explain why many still did not believe. He quotes language about the Lord's arm being revealed and then the difficult words about blinded eyes and hardened hearts.
The evangelist treats unbelief as both human refusal and a reality interpreted through Scripture.
Isaiah 53 asks who has believed the prophetic report and to whom the arm of the LORD has been revealed. Isaiah 6 describes a people whose hearing and perception have become hardened under judgment. In biblical idiom the heart is the center of thought, will, and moral response, not merely emotion. John's sequence should not be flattened into a denial of human responsibility; throughout the Gospel people are repeatedly summoned to believe even as persistent rejection is described in judicial terms.
The prophetic background places rejection of Jesus within a familiar biblical pattern: exposure to God's revelation does not automatically produce faith.
John holds together warning and sovereignty. Repeated refusal can become hardening, while the unbelief surrounding Jesus does not mean that God's purposes or the prophetic Scriptures have failed.