Matthew Henry Commentary Luke 18:31-34

"And he took unto him the twelve, and said unto them, Behold, we go up to Jerusalem, and all the things that are written through the prophets shall be accomplished unto the Son of man. For he shall be delivered up unto the Gentiles, and shall be mocked, and shamefully treated, and spit upon: and they shall scourge and kill him: and the third day he shall rise again. And they understood none of these things; and this saying was hid from them, and they perceived not the things that were said." — Luke 18:31-34 (ASV)

The Spirit of Christ, in the Old Testament prophets, testified beforehand to his sufferings and the glory that would follow (1 Peter 1:11). The disciples' prejudices were so strong that they would not understand these things literally. They were so intent on the prophecies that spoke of Christ's glory that they overlooked those that spoke of his sufferings.

People make mistakes because they read their Bibles by halves and are only interested in the smooth things. We are as reluctant to learn the proper lessons from the sufferings, crucifixion, and resurrection of Christ as the disciples were regarding what he told them about those events; and for the same reason: self-love and a desire for worldly objects close our understanding.