John 8:27

But they did not know that He spake unto them of the Father.

John 8:43

And why do ye not understand my language, but because ye cannot bear my doctrine?

John 8:47

He, that is of God, receiveth the words of God; but ye therefore receive them not, because ye are not of God.

Romans 11:7-10

What then? Israel hath not obtained that which he sought: but the elect have obtained it, and the rest were blinded,

2 Corinthians 4:3-4

And if our gospel also be veiled, it is to those 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
And why do ye not understand my language, but because ye cannot bear my doctrine?
Romans 11:7
What then? Israel hath not obtained that which he sought: but the elect have obtained it, and the rest were blinded,
2 Corinthians 4:3
And if our gospel also be veiled, it is to those that perish;