John 8:27

They did not understand that he spoke to them of the Father.

John 8:43

Why do you not understand what I say? It is because you are not able to hear my word.

John 8:47

He who is of God hears the words of God; the reason you do not hear them is that you are not of God."

Romans 11:7-10

What then? Israel did not obtain what it sought. The elect obtained it, but the rest were hardened,

2 Corinthians 4:3-4

And even if our gospel is veiled, it is veiled 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 not understand what I say? It is because you are not able to hear my word.
Romans 11:7
What then? Israel did not obtain what it sought. The elect obtained it, but the rest were hardened,
2 Corinthians 4:3
And even if our gospel is veiled, it is veiled to those who are perishing.