Mark 9:30-31 Leaving that region, they traveled through Galilee. Jesus tried to avoid all publicity in order to send more time with his disciples and teach them. He said to them, "The Son of Man is going to be betrayed. He will be killed, but three days later he will rise from the dead." But they didn’t understand what he was saying, and they were afraid to ask him what he meant.
Jesus knew that He was going to go to Calvary very soon. He knew that He had to spend as much alone time with the disciples as He could to help prepare them for His departure and life without Him. He did not want His ministry of helping people to get in the way of His finishing His discipleship training.
Jesus told them very clearly about His death and resurrection. It was important that they understood this core belief of the Gospel. If they did not get this, then there would be no Gospel for them to share after He had left them. Even though they did not yet understand what Jesus meant, the seed was sown and they did get it after it all came to pass.
Two things of interest grab me as I think about this. Unless we understand and own the truth of Jesus’ death and resurrection, we have no message to share. And, people don’t often understand what we say right away, but if we plant the seed in them, they will understand later on. It’s not our role to convince people of the truth of the Gospel, only the Holy Spirit can do that. Our role is to just share what we understand and commit the rest to God’s working in the heart and mind of others.
Also, if you don't understand some things the Lord is teaching you, don't sweat it. Those things you need to know you will know in time. Those things you don't need to know just accept them by faith. Know that they are true because God says it and He cannot lie.