When Peter spoke the Word he spoke for God. Later, when Peter spoke from the opinion of the world, he allowed Satan to speak through him. Good Christians often allow their sinful opinions to stir up trouble in their homes and in their congregations. To the extent that their opinions go against sound doctrine and threaten the unity of the church and the family, these Christians are in those moments working for Satan's ends whether they know it or not. People aren't the only ones who have opinions.
Whole cultures have opinions that prevail in the public thinking.
But the Word of God is counter-cultural. The Word tells us to believe things that go against the flow of current thinking. When Peter confesses that Jesus is the Christ, he confesses it alone. Not even the other disciples were ready to say this about Jesus yet. One of my favorite saints from another century is Athanasius who lived in the third century.