[Jesus] said to them, But who do you [yourselves] say that I am? Simon Peter replied, You are the Christ, the Son of the living God. Matthew 16:15-16 — Matthew 16:15-16
When Peter said that Jesus was the Christ, the Son of the living God, it was a statement of faith. In making this statement, Peter was displaying faith.
I don’t think Peter just casually or nonchalantly made that statement. I think he did it with a surety and a certainty that impressed Jesus because He immediately turned to Peter and told him that he was blessed. Then He went on to say that it was upon this rock-solid foundation of faith that He would build His church.