Matthew Poole and continuators on John 10:6

6 This parable spake Jesus unto them: but they understood not what things they were which he spake unto them .

Our Saviour was wont to instruct them in the Mysteries of the Kingdom of God by Parables; that is, Similitudes taken from reasonable actions of men, which might be, and were proper to express Spiritual things by: wherefore he used this Method in Teaching, we are told, Matth 13, 10, 11, 12, 13. They well enough understood the words in which those Parables were delivered; but the Inward Sense, the Spiritual Mysteries shadowed out in those Similitudes: these they understood not, neither the common sort of his Disciples understood them, nor did the better sort of his Disciples understand them, without a further explication of them. Our Lord therefore in the following verses, comes to give them a large explication of the Parable.