John 8:27

They did not realize [or have the spiritual insight to understand] that He was speaking to them about the Father.

Isaiah 6:9

And He said, “Go, and tell this people:

‘Keep on listening, but do not understand;
Keep on looking, but do not comprehend.’

Isaiah 42:18-20


Hear, you deaf!
And look, you blind, that you may see.

Isaiah 59:10


We grope for a wall like the blind,
We grope like those who have no eyes.
We stumble at midday as in the twilight;
Among those who are healthy we are like dead men.

John 8:43

Why do you misunderstand what I am saying? It is because [your spiritual ears are deaf and] you are unable to hear [the truth of] My word.

John 8:47

Whoever is of God and belongs to Him hears [the truth of] God’s words; for this reason you do not hear them: because you are not of God and you are not in fellowship with Him.”

Romans 11:7-10

What then? Israel failed to obtain what it was seeking [that is, God’s favor by obedience to the Law], but the elect [those chosen few] obtained it, while the rest of them became hardened and callously indifferent;

2 Corinthians 4:3-4

But even if our gospel is [in some sense] hidden [behind a veil], it is hidden [only] to those who are perishing;

Treasury of Scripture Knowledge

Summary

They understood not that he spake to them of the Father.

Bible References

General references

John 8:43
Why do you misunderstand what I am saying? It is because [your spiritual ears are deaf and] you are unable to hear [the truth of] My word.
Isaiah 6:9
And He said, “Go, and tell this people:

‘Keep on listening, but do not understand;
Keep on looking, but do not comprehend.’
Isaiah 42:18

Hear, you deaf!
And look, you blind, that you may see.
Isaiah 59:10

We grope for a wall like the blind,
We grope like those who have no eyes.
We stumble at midday as in the twilight;
Among those who are healthy we are like dead men.
Romans 11:7
What then? Israel failed to obtain what it was seeking [that is, God’s favor by obedience to the Law], but the elect [those chosen few] obtained it, while the rest of them became hardened and callously indifferent;
2 Corinthians 4:3
But even if our gospel is [in some sense] hidden [behind a veil], it is hidden [only] to those who are perishing;