Well ... that is a loaded question Isaiah.

Who is blind except my servant, So deaf as the messenger I send?

Who is so blind as the one rewarded, So blind as the servant of Jehovah?

• Isaiah 42:19

Let's unwind this a bit.

Followers of Jehovah God are the only humans not completely blinded by "the god of this world"; a basic biblical concept really.

"The god of this age has blinded the minds of unbelievers, so that they cannot see the light of the gospel that displays the glory of Christ, who is the image of God."

• 2 Cor 4:4

Therefore Isaiah must be talking about a different form of "blindness".

Here is what follows:

"You see many things, but you do not keep watch. You open your ears, but you do not listen."

• Isaiah 42:20

Now the statement makes sense; that extreme blindness is actually a function of only seeing to a point, and then "turning off the brain" so to speak.

This gives meaning to what Jesus stated at Matthew 6:23:

"But if your eyes are unhealthy, your whole body will be full of darkness. If then the light within you is darkness, how great is that darkness!"

Isn't this true? When we see enough to identify our personal sinful nature, but "stop listening" we are prone to judgment. "great darkness"

The history of Christendom really can be summed up by this concept; seeing enough to "know" but not enough to handle it correctly.