What does the Bible say about the blindness of sinners?

2 Corinthians 4:3-4 states that if our gospel is veiled, it is veiled to those who are lost. The reason for this blindness is that the God of this world has blinded the minds of the unrepentant, preventing them from seeing the light of the glorious gospel of Christ. This indicates that spiritual blindness is not merely a lack of awareness but an active resistance to the truth of the gospel. Sinners in their natural state are described as lost, blind, and unbelieving, unaware that they are separated from God and unable to seek Him on their own.