What does Matthew 17:22 mean?

Jesus and the disciples are gathering in Galilee. This may refer to their return to Galilee from Caesarea Philippi in the north (Matthew 16:13). It might also mean re-gathering after being separated into two groups, with Peter, James, and John following Jesus to the top of the mountain for the transfiguration (Matthew 17:1–2).

This is not the first time that Christ has mentioned His coming death and resurrection. Matthew 16:21 mentions a recent incident where He referred to this impending series of events. This was the moment Peter tried to rebuke Jesus and Jesus rebuked Peter, instead, as if he were Satan (Matthew 16:22–23).

Now, Jesus adds a new detail about what will soon happen to Him. He says that He, "the Son of Man," is about to be delivered into the hands of men. In other words, someone is going to turn Jesus over to the people who will kill Him. It's not clear from this verse if Jesus means that the one doing the delivering will be Judas in his betrayal of Jesus or, perhaps, God the Father in His work of offering Jesus as the sacrifice for sin.

What's clear is that, though the disciples are distressed by Jesus saying this, they still don't understand what He means.