And even if our gospel is veiled, it is veiled to those who are perishing. In their case the god of this world has blinded the minds of the unbelievers, to keep them from seeing the light of the gospel of the glory of Christ, who is the image of God. (2 Corinthians 4:3-4 ESV)
In context, Paul has said that he plainly and straightforwardly proclaims the truth, the whole truth, and nothing but the truth about God. He has nothing bearing upon him to cause him to compromise it. Therefore, the only ones who cannot see clearly what he has clearly presented are those who are blind to see it. They do not have eyes to see or ears to hear. They are incapable of seeing what is plainly in front of their faces.
Paul explains this as being blinded by the god of this world. Most commentators say this god is Satan, which does not mean that he is a god, for there is only one God. But rather that he has taken the place of God. It is possible to understand the god of this world as the world (i.e. an epexegetical genitive--the god which is this world). This would not mean the physical world, but the world as it is understood and acted within apart from God. Any concept of that world that excludes God would require substituting idols for God. Therefore, Satan would still be the god of that world, which means that regardless, all this still points back to Satan’s involvement.
It is possible that the blinding activity of Satan is both/either continuous and/or past (perfect). I am sure Satan is actively blinding people continuously in this world, shading the light of Christ. However, this activity is not required for people to be continuously blind. It is probable that this refers mainly to what Satan did in the garden when he suggested idolatry to Adam and Eve, and they chose the created thing over the creator. The effect was the Fall and a depraved, blinded state for all who descended from Adam. So we need not posit that every and all instances of blindness require the immediate activity of Satan. Sufficient blinding was accomplished through his contribution to the Fall. All other activity is just repair and maintenance on the work he already accomplished.
These people are described as “perishing,” a state that is remediable only by God’s shining “in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ (v. 6).” Without this, they will remain blind, under the effects of Satan’s blinding work, whether past and universal or present and individual.
Questions often arise about how this fits in with predestination, as in “how is this fair to those who have no fault in their own blindness, if it is indeed Satan who has blinded them?”
This dilemma of fairness is resolved by pointing out (whether we like it or not) that Scripture teaches that we are always to blame for our own sinfulness. Therefore we are always to blame for our own blindness. A blinding god of this world is a god we have chosen to worship instead of the one true God. We have preferred blindness over sight. It is no less fair that we were included federally in Adam and his sin in the beginning when the blindness was first introduced. Satan will have his judgment for his role in blinding the world, and we will be judged for loving our blindness.