Second Prediction of the Passion

Everything that Jesus did claimed admiration from all men for a peculiar and divine light reflected upon each; of His works, according to the Psalms, honor and majesty will you lay upon him. Although all indeed marveled at those things which He did, He however addresses what follows, not to all, but to His disciples. He had shown His glory on the mount to His disciples, and after this delivered a man from an evil spirit, but it was necessary for Him to undergo His passion for our salvation. Now His disciples might have been perplexed, saying, "Have we then been deceived in that we thought him to be God?"

That they might know then what was to happen to Him, He bids them lay up in their minds as a certain deposit the mystery of His passion, saying, "Let these sayings sink down in your hearts." By the word your, He distinguishes them from others. For the multitude were not to know that He was about to suffer, but were rather to be assured that the dead would rise again, destroying death, lest they should be offended.

Now some perhaps will say, How were the disciples ignorant of the mystery of the cross, seeing that it was touched upon in several places by the shadows of the Law? But as Paul relates, "Even to this day, when Moses is read, the veil is upon their hearts." (2 Cor. 3:14) Our duty, therefore, is to draw near God, and say, "Open my eyes to see clearly the wonders of your law." (Psalms 119:18) So He will reveal Christ to us: by Whom and with Whom to God the Father be praised and dominion with the Holy Spirit, for ever and ever, Amen.

References:
Catena Aurea (St. Thomas Aquinas)
Sermon 53, Commentary on Luke (St. Cyril of Alexandria)