John 16:18
So they kept on repeating, "What is the meaning of what he says, 'In a little while'? We do not understand what he is talking about."
Matthew 16:9-11
Do you still not understand? Don't you remember the five loaves for the five thousand, and how many baskets you took up?
Luke 24:25
So he said to them, "You foolish people -- how slow of heart to believe all that the prophets have spoken!
Hebrews 5:12
For though you should in fact be teachers by this time, you need someone to teach you the beginning elements of God's utterances. You have gone back to needing milk, not solid food.