Matthew 16:16

And Simon Peter answered and said, Thou art the Christ, the Son of the living God.

This is called the Great Confession. It is no mere acknowledgment that Jesus is the Messiah of the Hebrews but also declares Jesus' unique filial relationship to God. Dummelow aptly pointed this out, saying,

Son of God, here, is no mere equivalent of "the Messiah." ... This is shown by the deep emotion with which the speaker makes, and Jesus receives, the confession; and the fact that the confession is perfectly satisfactory to Jesus, and is forthwith made the dogmatic foundation of Christianity ("Upon this rock I will build my church.").[6]

The ancients noted the expression, "Son of the living God," making those words the basis of Jesus' blessing of Peter. Thus, Origen said, "He is pronounced blessed not merely because he said, `Thou art the Christ,' but with the addition, `Son of the living God'."[7] Origen reinforced his argument by pointing out that Mark and Luke, omitting the words "Son of the living God," also omitted reference to Christ's blessing Peter on that occasion.

[6] Ibid.

[7] Origen, Commentary on Matthew in the Ante-Nicene Fathers, Vol. X, p. 460.