Jesus is the Son and Jesus must Suffer
Two principles arise from this passage. The first is that Jesus is the Son of God (v13-20). The second is that Jesus must Suffer (v21). Jesus instructed the disciples in who he was. It's here that Peter gives us his great confession, that Jesus is the Christ, the son of the living God. The question that must be answered first is who Jesus is before we see that he must suffer.
We must establish who Christ is so we can attach value to his suffering. Once we see that he's the son of the living God we can see that his suffering had value and merit. Many men were crucified before Jesus but because they were sinners their value had no atoning value. Since Christ we sinless and perfect his sacrifice and suffering had redemptive value.
His suffering included crucifixion on the cross. On the cross Christ atoned for man's sin. He experienced separation from his father for a moment for us so we can experience an eternity with him. He experienced the wrath of God for a moment for us so we can experience the love of the father.
If you don't believe that Jesus is the son of the living God and has suffered fur you you can become a child of God by faith in the Lord Jesus Christ.
Jesus said in John 3:16, "For God so loved the world, that he gave his only begotten Son, that whosoever believes in him should not perish, but have everlasting life."
Jesus is the son of the living God and has suffered.