John 8:27

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

John 8:43

Why do ye not understand my language? It is because ye cannot listen to my word.

John 8:47

He that is of God heareth Gods words; for this cause ye do not hear, because ye are not of God.

Romans 11:7-10

What Israel seeketh after, that Israel did not obtain; but the elect obtained it, and the rest were hardened;

2 Corinthians 4:3-4

But if our gospel is veiled, it is veiled to them that perish,

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 ye not understand my language? It is because ye cannot listen to my word.
Romans 11:7
What Israel seeketh after, that Israel did not obtain; but the elect obtained it, and the rest were hardened;
2 Corinthians 4:3
But if our gospel is veiled, it is veiled to them that perish,