John 10:6

‘This mysterious saying Jesus spoke to them, but they did not understand what things they were that he spoke to them.”

The people did not have centuries of understanding behind them, and so they were puzzled. They did not know what He meant. We can understand this. The total uniqueness of Jesus had not yet dawned on them. They still thought in terms of the Law as expounded by the religious teachers. But that was Jesus' point. Many of those teachers were simply ‘thieves and robbers', stealing the truth from them.