I have had the opportunity to lead the Builders Sunday Morning Small Group for three weeks studying the gospel according to Mark. This question was from a breakout group studying Mark 8:27-30.
Peter’s confession is the first human confession that is recorded in Mark. To this point in the narrative the naming of Jesus identity had come from demons that had been cast out by Jesus.
I think that Peter knew what he was saying. He would have likely had some understanding of the expectation for a messiah and what that might look like. However, I do not think that Peter understood the depths of the truth that he was saying and the nuances of how this would actually take place.
There are two places where I think Peter may not have fully understood what he was saying. Jesus is savior not just for the Jewish people, but for all of creation. Also, suffering was a key part of Jesus journey to resurrection.
You can find previous responses to questions coming from this class here:
Rev. Andrew Conard 
3 replies on “Did Peter know what he meant by saying, “You are the Christ?””
[…] Did Peter know what he meant by saying, “You are the Christ?” […]
I think that the Holy spirit gave Peter the intellect to say the right thing and that because of this Peter knew what he was saying.
Gary – Good call. As a friend on staff said recently – “We will trust the Holy Spirit to do what the Holy Spirit does.”