Isaiah is told to speak in a way that results in ongoing hearing without understanding and seeing without perceiving (Isaiah 6:9). The passage describes hearts dulled, ears heavy, and eyes shut so they do not turn and be healed (Isaiah 6:10).
In Isaiah 6:9–10 Isaiah is sent with a message that exposes Israel’s refusal to respond. The people will keep hearing words and seeing events, yet they will not grasp what they mean. The commission describes their inner life as dulled and closed off: hearts thickened, ears weighed down, eyes shut. These lines come directly after Isaiah’s vision of the Lord in the temple and his commissioning as a messenger (6:1–8). Having been purified and having volunteered to be sent, Isaiah then receives an unusually negative-sounding assignment: his preaching will not produce quick understanding.
Isaiah 6:9–10 presents Isaiah’s commission as a paradox: he is sent to speak God’s words, yet the expected result is continued exposure without real grasp. The people will “hear” and “see” repeatedly, but not arrive at understanding or perception.
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Isaiah 6:9, then read the surrounding section so the answer stays connected to the passage's flow.
9He said, Go, and tell this people, Hear you indeed, but don`t understand; and see you indeed, but don`t perceive.