Jesus was taking His disciples up to Jerusalem for the Passover celebration there. While there, the Son of Man would somehow be delivered over to the chief priests and scribes, His antagonistic opponents. This implied a betrayal (cf. Matthew 17:22). They would condemn Him to death. This implied legal proceedings. He would fall under the control of the Gentiles who would ridicule, torture, and crucify Him. The Romans were the only Gentiles with authority to crucify; the Jews did not have this power under Roman rule. Three days later Jesus would be raised up to life. [source][source][source]
This was Jesus" third and most specific prediction of His death ( Matthew 16:21; Matthew 17:22-23; cf. Matthew 12:40; Matthew 16:4; Matthew 17:9). He mentioned for the first time the mode of His death, crucifixion, and the Gentiles" part in it. Jesus" ability to predict His own death was another indication of His messiahship. His willingness to proceed toward Jerusalem in view of what lay before Him shows that He was the Suffering Servant obedient even to death on a cross. [source][source][source]
"These three passion-predictions are the counterpart to the major summary-passages found in the second part of Matthew"s story ( Matthew 4:23; Matthew 9:35; Matthew 11:1). The function they serve is at least twofold. On the one hand, they invite the reader to view the whole of Jesus" life story following Matthew 16:21 from the single, overriding perspective of his passion and resurrection. On the other hand, they also invite the reader to construe the interaction of Jesus with the disciples throughout Matthew 16:21 to Matthew 28:20 as controlled by Jesus" concern to inculcate in them his understanding of discipleship as servanthood ( Matthew 16:24-25; Matthew 20:25-28)." [1][source]