Mark 8:21

And He was saying to them, “Do you still not understand?”

Mark 6:52

because they had not understood [the miracle of] the loaves [how it revealed the power and deity of Jesus]; but [in fact] their heart was hardened [being oblivious and indifferent to His amazing works].

Psalm 94:8

Consider thoughtfully, you senseless (stupid ones) among the people;
And you [dull-minded] fools, when will you become wise and understand?

Matthew 16:11-12

How is it that you fail to understand that I was not talking to you about bread? But beware of the leaven of the Pharisees and Sadducees.”

Mark 8:12

He groaned and sighed deeply in His spirit and said, “Why does this generation demand a sign? I assure you and most solemnly say to you, no sign will be given to this generation!”

Mark 8:17

Jesus, aware of this [discussion], said to them, “Why are you discussing [the fact] that you have no bread? Do you still not see or understand? Are your hearts hardened?

Mark 9:19

He replied, “O unbelieving (faithless) generation, how long shall I be with you? How long shall I put up with you? Bring him to Me!”

John 14:9

Jesus said to him, “Have I been with you for so long a time, and you do not know Me yet, Philip, nor recognize clearly who I am? Anyone who has seen Me has seen the Father. How can you say, ‘Show us the Father?’

1 Corinthians 6:5

I say this to your shame. Can it be that there is not one wise man among you who [is governed by integrity and] will be able and competent to decide [private disputes] between his fellow believers,

1 Corinthians 15:34

Be sober-minded [be sensible, wake up from your spiritual stupor] as you ought, and stop sinning; for some [of you] have no knowledge of God [you are disgracefully ignorant of Him, and ignore His truths]. I say this to your shame.

Treasury of Scripture Knowledge

Summary

Mark 8:21

And he said unto them, How is it that ye do not understand?

How

General references

Matthew 16:10

Bible References

How