Spiritual truth is in short supply in our era of politically correct speech, carefully crafted answers, and plain old stretching and hedging the truth. Jesus, however, is very plain about his future. There is nothing hidden or fancy.
Jesus' simple and direct speech makes his forecast even more shocking. So at Jesus' first self-revelation about the cross, Peter rebuked him and would not allow Jesus to prophesy his future because it "couldn't be true" that the Messiah would go to the cross. But this was God's plan. This is God's truth.
Thankfully for Jesus, the disciples are beginning to hear a little more carefully and they pick up on the sense of impending confrontation and battle at the cross. This time they hear Jesus' message and instead of responding with a stern rebuke of their Master, they are very sorrowful.
It is never easy to mature people beyond their prejudices and biases. But Jesus reminds us that while the growth may be slow, the victory can be very sweet. While the disciples are not all the way to understanding the cross, they have at least begun their journey!