They did not comprehend the things that were said.

Luke 18:31-34, And He took the twelve aside and said to them, "Behold, we are going up to Jerusalem, and all things which are written through the prophets about the Son of Man will be accomplished. For He will be delivered to the Gentiles, and will be mocked and mistreated and spit upon, and after they have scourged Him, they will kill Him; and the third day He will rise again." And they understood none of these things, and this saying was hidden from them, and they did not comprehend the things that were said.

The disciples could not make sense out of what Jesus was saying, and indeed even from this side of the cross it is hard to really comprehend all that God has done for us. The very nature of faith is hard to comprehend, why one hears the word and has faith and another does not. Why one is convicted of his own need for a Savior, and another is fully convinced of his own self-righteousness. If the disciples who walked with Jesus had trouble understanding, it is understandable that we might as well.

Come, Holy Spirit, bring Your light into every situation; help me to be faithful in that which You call me to do.