A.T. Robertson 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)

And they perceived not (κα ουκ εγινωσκον). Imperfect active. They kept on not perceiving. Twice already Luke has said this in the same sentence.

They understood none of these things (ουδεν τουτων συνηκαν). First aorist active indicative, a summary statement.

This saying was hid from them (ην το ρημα τουτο κεκρυμμενον απ' αυτων). Past perfect passive indicative (periphrastic), state of completion. It was a puzzling experience. No wonder that Luke tries three times to explain the continued failure of the apostles to understand Jesus. The words of Christ about his death ran counter to all their hopes and beliefs.