Matthew 16:7

And they reasoned among themselves, saying, We took no bread. And Jesus perceiving it said, O ye of little faith, why reason ye among yourselves, because ye have no bread?

The need of Jesus' warning appeared in the fact that, even at that late hour, the apostles were far too literal in construing the words of Christ. The Saviour's warning against the Pharisees might have gone unheeded if Christ had not explained it. Far from catching the significance of his words, at first they thought that they were being scolded for forgetting to buy bread.

Just where the above conversation took place is a matter of different opinions. It might have been on board en route to Bethabara-Julius, or after they landed; what difference could it make? Like disciples of old, men can still find a lot to be concerned about, besides the point! Christ knew what was in the disciples' minds, no less than he knew what was in the Pharisees' minds. Only God has such power.