blinded = hardened, as Pharaoh (Romans 9:18) — God’s retribution
spirit of slumber (stupor) from Isaiah 29:10 — For the LORD hath poured out upon you the spirit of deep sleep, and hath closed your eyes: the prophets and your rulers, the seers hath He covered. The rest of the verse is from Deuteronomy 29:4 — Yet the LORD hath not given you an heart to perceive, and eyes to see, and ears to hear, unto this day.
Israel wasn’t blind. They knew they weren’t following God but were seeking their own righteousness. As a result, they were blinded.
First, we are told that Israel failed to obtain that for which it was seeking. We are told elsewhere that Israel was seeking after righteousness. We have already seen that they had a zeal for God but that it was not according to knowledge. They were ignorant of the righteousness that comes from God and, as they were trying to establish their own righteousness, they did not submit to the righteousness of God (10:2-3). We have seen that their own Scriptures showed the way of righteousness but that they were not willing to accept it. If they had called on the name of the Lord, they would have been saved, but they were so proud of their own efforts that they would not stoop to take things in God’s way. — Barnhouse, pages 115-116.