Luke 9:45
But they understood not this saying, and it was hid from them, that they perceived it not: and they feared to ask him of that saying. But they understood not this saying, and it was hid from them, that they perceived it not: and they feared to ask him of that saying.
This saying belongs to Christ's final instructions before He was taken from His disciples. It concerned what lay ahead for Him, namely His coming suffering, which the disciples did not understand or perceive. Its meaning was hidden from them.
Their lack of understanding persisted despite what Jesus had already told them. The knowledge was unwelcome to them, and self-pity made them shrink from sharing His suffering. Peter's protest against that suffering expressed the thought and feeling of all twelve.
Sorrow over His words about the future made them unwilling to ask Him to explain it, and they feared to ask. They were reluctant to face what He foretold because they thought it might not happen. They needed to remember His words and understand His work, studying the Word and preparing to follow Him through coming trials and persecutions. Their understanding was to grow continually, like increasing light.