Summary: receiving or not receiving spiritual sight
All through Scripture, blindness is used to represent the spiritual inability to see God's truth. As a man is physically blind, he cannot see God's visible revelation. That is he can't see the trees and the earth and the sky. But as a man is spiritually blind, he cannot see God's invisible revelation; love, truth, holiness, forgiveness, blessing, eternal life, grace, joy, peace, etc. As the blind eye cannot see light, so the blind spirit cannot see the light, the light of the world, Jesus Christ.
This is the theme of this unusually long story in chapter 9 of John's gospel.
Apostle Paul characterizes the whole scheme of salvation by making a comparison to blindness. In verse 3 of 2 Corinthians 4, Paul says, "If our gospel be hidden, it is hidden to them that are lost." .
Later on in verse 6, Paul says it is we Christians who have seen the light. God has commanded in us that light should shine out of darkness. But in the case of unbelievers, they are in darkness, their minds blinded by the God of this world to prevent the light of the gospel from shining unto them. And thus it is hidden to them. When salvation comes along, it opens the eyes of the soul or the spirit to understand light and to comprehend God's truth.
This is clearly illustrated by Paul when he was talking to Agrippa in the twenty-sixth chapter of Acts. He says this, "I came to open their eyes and turn them from darkness to light." That was Paul's mission, to take spiritually blind people and give them spiritual sight. Now the scriptures teach us that it is only those who know and love Jesus Christ who have spiritual sight. There are a lot of people in the world who are religious and think they see. The Pharisees did. They were super religious. They thought they could see and comprehend every spiritual truth in existence. But, they were totally blind. Rather than people being in a religion and finding light, they veil themselves in darkness and we find it difficult to break through, we cannot--apart from God--commanding the light to shine out of that darkness. And we'll see how that works in a few minutes.
Light is the possession of God? God is..what?...light. And in Him there is no darkness at all. And the Apostle Paul carefully points this out, 1 Thessalonians 5, "But of the times and the seasons, brethren, you have no need that I write unto you." "For you yourselves know perfectly that the day of the Lord comes as a thief in the night when they all say peace and safety, then sudden destruction cometh upon them, there's travail upon a woman with child and they shall not escape. But ye, brethren, are not in darkness that the day should overtake you as a thief, you are sons of light and sons of the day." You who know Christ, you are the sons of light.
And then the Apostle Paul also writing to the Colossians said this, "Giving thanks unto the Father who hath made us fit to be partakers of the inheritance of the saints in light, who hath delivered us from the power of darkness and hath translated us into the Kingdom of His dear Son." The only people who know light are those who know Jesus Christ, for His is the kingdom of light.