Jesus explains to his disciples that he must “go to Jerusalem and suffer many things from the elders and chief priests and scribes, and be killed, and on the third day be raised” (Mt 16:21).
Everything seems to have been turned upside down in the disciples' hearts! How could “the Christ, the Son of the living God” (v. 16) suffer unto death? The Apostle Peter rebels, he refuses to accept this route, he rebukes the Teacher saying: “God forbid, Lord! This shall never happen to you” (v. 22). The divergence between the Father's loving plan — which even went as far as the gift of the Only-Begotten Son on the Cross to save humanity — and the disciples' expectations, wishes and projects stands out clearly. And today too this contrast is repeated: when the fulfilment of one's life is geared solely to social success and to physical and financial well-being, one no longer reasons according to God but according to men (v. 23).
Thinking as the world thinks is to set God aside, not accepting his plan of love, preventing him, as it were, from doing his wise will. For this reason Jesus says some particularly harsh words to Peter: “Get behind me, Satan! You are a hindrance to me” (ibid.). The Lord teaches that “the way of discipleship [is] the way to follow him [walk behind him], the Crucified. In all three Gospels he also interprets this ‘following’ on the way of the Cross” as “the indispensable way for man to ‘lose his life’, without which it is impossible for him to find” himself” (Jesus of Nazareth, English edition, New York, p. 287).
As he invited the disciples, Jesus also addresses an invitation to us: “If any man would come after me, let him deny himself and take up his cross and follow me” (Mt 16:24). A Christian follows the Lord when he accepts lovingly his own cross, which in the world's eyes seems a defeat and to “lose life” (cf. vv. 25-26), knowing that he is not carrying it alone but with Jesus, sharing his same journey of self-giving.
The Servant of God Paul VI wrote: “In a mysterious way, Christ himself accepts death... on the Cross, in order to eradicate from man's heart the sins of self-sufficiency and to manifest to the Father a complete filial obedience” (Apostolic Exhortation Gaudete in Domino, 9 May 1975). By willingly accepting death, Jesus carries the cross of all human beings and becomes a source of salvation for the whole of humanity.
St Cyril of Jerusalem commented: “The glory of the Cross led those who were blind through ignorance into light, loosed all who were held fast by sin and brought redemption to the whole world of mankind” (Catechesis Illuminandorum XIII, 1: de Christo crucifixo et sepulto: PG 33, 772 B).
[Pope Benedict, Angelus, 28 August 2011]