3 Our Lord Jesus Christ erewhile became Man, but by the many He was unknown. Wishing, therefore, to teach that which was not known, He called together His disciples, and asked them, Whom do men say that I, the Son of Man, am? — not from vain-glory, but wishing to show them the truth, lest dwelling with God, the Only-begotten of God, they should think lightly of Him as if He were some mere man. And when they answered that some said Elias, and some Jeremias, He said to them, They may be excused for not knowing, but you, My Apostles, who in My name cleanse lepers, and cast out devils, and raise the dead, ought not to be ignorant of Him, through whom you do these wondrous works.
And when they all became silent (for the matter was too high for man to learn), Peter, the foremost of the Apostles and chief herald of the Church, neither aided by cunning invention, nor persuaded by human reasoning, but enlightened in his mind from the Father, says to Him, You are the Christ, not only so, but the Son of the living God. And there follows a blessing upon his speech (for in truth it was above man), and as a seal upon what he had said, that it was the Father who had revealed it to him.
For the Saviour says, Blessed are you, Simon Barjona, for flesh and blood has not revealed it to you, but My Father which is in heaven. He therefore who acknowledges our Lord Jesus Christ the Son of God, partakes of this blessedness; but he who denies the Son of God is a poor and miserable man.
Source: Catechetical Lectures (New Advent)