From that time on Jesus began to show his disciples that he must go to Jerusalem and suffer many things at the hands of the elders, chief priests, and experts in the law, and be killed, and on the third day be raised.
[Matt 16:21 NET]
It is always painful to speak to one’s friends of one’s coming sufferings or death.
It must have been hard for Jesus to break to His disciples, in their enthusiasm and hope, the fact of which He now speaks to them. He knew how it would disappoint and grieve them. But it was time they should learn the true nature of His Messiahship. All their Messianic expectations were of one who should be a great King, establishing a universal empire.
The word “must” in our Lord’s announcement is important – He must suffer. This was the way marked out for the Messiah in Old–Testament prophecies. He was not to be invested with mere human glory and to follow out men’s ideas of greatness. He should bless the world by giving Himself for it.
There could be no redemption for men but by the atonement, and the Son of God was the only one who could make this atonement. We must never forget that the cross was an essential element in Christ’s work as Saviour.