Luke 9:45

However this announcement did not make sense to the disciples. This was probably because of the popular view of the Messiah that still influenced them, the glorious prophecies about the Son of Man in the Old Testament, and Jesus’ great popularity. Most important they did not understand because God hid this understanding from them (cf. Luke 24:16). That is, they understood the words but could not understand how this would happen, partly because of their limited faith. They remembered Jesus’ words, but they only understood the prediction after Jesus’ resurrection. Perhaps they were afraid to ask Jesus to clarify what He said because they feared to hear what they suspected, that Jesus would indeed die soon.

"Some interpreters understand the statement, ’It was hid from them that they might not understand it,’ as indication that God prevented the disciples from understanding. [Note: Footnote 39: See, e.g., R. J. Dillon, "Previewing Luke’s Project from His Prologue (Luke 1:1-4)," Catholic Biblical Quarterly 43 (1981):216.] While the passive formulation may hint at divine involvement, I would caution against the assumption that human resistance is not an important factor at this point in the narrative. If a divine purpose is involved, it is a purpose which works in and through human resistance, for which humans remain responsible." [Note: Tannehill, 1:227.]

Thus there was a "suffering secret" as well as a "messianic secret" in Jesus ministry. [Note: Marshall, The Gospel . . ., p. 393.] The "messianic secret" was the fact that Jesus was the divine Messiah, which He revealed only gradually before the Triumphal Entry. He withheld this information to preclude superficial and premature acceptance of Himself by the multitudes. The "suffering secret" was the information about Jesus’ passion that God revealed to the disciples only gradually before the Resurrection.