It is Peter who most frequently responds and answers for the group. A reader of the Gospels almost begins to picture, when Jesus asks a question, that the other disciples glance over to Peter to see whether he will respond. It is almost as if they defer to him. Though this is not specifically written in Scripture, it seems to be their thinking regarding him.
John W. Ritenbaugh
Unity (Part 2): God's Pattern of Leadership
Peter proclaims Jesus to be the Messiah, and Jesus speaks of building His church and being crucified and resurrected. This was a major step forward in the disciples' understanding, and it corrected the erroneous prophetic teaching of the Pharisees and Sadducees. However, from the incident that occurs in verses 22-23, we can see that Peter—and probably the other disciples also—were not yet fully convinced of it.
Richard T. Ritenbaugh
Why the Transfiguration?
Other Forerunner Commentary entries containing Matthew 16:16: