And taking the twelve, he said to them, “See, we are going up to Jerusalem, and everything that is written about the Son of Man by the prophets will be accomplished. For he will be delivered over to the Gentiles and will be mocked and shamefully treated and spit upon. And after flogging him, they will kill him, and on the third day he will rise.” But they understood none of these things. and this was the matter that was hidden from them, and they did not grasp the things that were spoken. [καὶ ἦν τὸ ῥῆμα τοῦτο κεκρυμμένον ἀπ’ αὐτῶν καὶ οὐκ ἐγίνωσκον τὰ λεγόμενα.] As he drew near to Jericho, a blind man was sitting by the roadside begging. And hearing a crowd going by, he inquired what this meant. They told him, “Jesus of Nazareth is passing by.” And he cried out, “Jesus, Son of David, have mercy on me!” And those who were in front rebuked him, telling him to be silent. But he cried out all the more, “Son of David, have mercy on me!” And Jesus stopped and commanded him to be brought to him. And when he came near, he asked him, “What do you want me to do for you?” He said, “Lord, let me recover my sight.” And Jesus said to him, “Recover your sight; your faith has made you well.” And immediately he recovered his sight and followed him, glorifying God. And all the people, when they saw it, gave praise to God.
Yet this business about the disciples not understanding what Jesus said here is Luke's addition to the narrative. It is not present in the original narrative Luke stole from Mark:
And they were on the road, going up to Jerusalem, and Jesus was walking ahead of them. And they were amazed, and those who followed were afraid. And taking the twelve again, he began to tell them what was to happen to him, saying, “See, we are going up to Jerusalem, and the Son of Man will be delivered over to the chief priests and the scribes, and they will condemn him to death and deliver him over to the Gentiles. And they will mock him and spit on him, and flog him and kill him. And after three days he will rise.”
Nor was it added by Matthew:
And as Jesus was going up to Jerusalem, he took the twelve disciples aside, and on the way he said to them, “See, we are going up to Jerusalem. And the Son of Man will be delivered over to the chief priests and scribes, and they will condemn him to death and deliver him over to the Gentiles to be mocked and flogged and crucified, and he will be raised on the third day.”
I am struck by the words καὶ ἦν τὸ ῥῆμα τοῦτο κεκρυμμένον ἀπ’ αὐτῶν. Is Luke really meaning that the disciples didn't understand that Jesus was going to die in Jerusalem. This seems hard to believe. Irenaeus tells us repeated in Book Three of Against Heresies that accepting the Gospel of Luke is key to salvation. He doesn't say this about Mark, Matthew or John. The heretics (not just the Marcionites but many heretics) objected to things that were put into the text. I wonder if the 'matter' here was the addition to Secret Mark.