Albert Barnes Commentary Luke 18:34

"And they understood none of these things; and this saying was hid from them, and they perceived not the things that were said." — Luke 18:34 (ASV)

Understood none of these things. Although these things were plainly revealed, yet their prejudices and their unwillingness to believe them were such that they did not understand them. They expected that he would be a temporal prince and a conqueror, and they were not willing to believe that he would be delivered into the hands of his enemies. They did not see how that could be consistent with the prophecies.

To us now, these things appear plain, and we can therefore learn that those things which seem most mysterious to us may yet appear perfectly plain; and we should learn to trust in God, and believe exactly what he has spoken; see Barnes on Matthew 16:21.