4 The Lord Himself, too, makes it evident who it was that suffered; for when He asked the disciples, “Who do men say that I, the Son of man, am?” and when Peter had replied, “You are the Christ, the Son of the living God;” and when he had been commended by Him [in these words], “That flesh and blood had not revealed it to him, but the Father who is in heaven,” He made it clear that He, the Son of man, is Christ the Son of the living God. “For from that time forth,” it is said, “He began to show to His disciples, how that He must go unto Jerusalem, and suffer many things of the priests, and be rejected, and crucified, and rise again the third day.” He who was acknowledged by Peter as Christ, who pronounced him blessed because the Father had revealed the Son of the living God to him, said that He must Himself suffer many things, and be crucified; and then He rebuked Peter, who imagined that He was the Christ as the generality of men supposed [that the Christ should be], and was averse to the idea of His suffering, [and] said to the disciples, “If any man will come after Me, let him deny himself, and take up his cross, and follow Me. For whosoever will save his life, shall lose it; and whosoever will lose it for My sake shall save it.” For these things Christ spoke openly, He being Himself the Saviour of those who should be delivered over to death for their confession of Him, and lose their lives.
Source: Adversus haereses (New Advent)