What does Mark 8:29 mean?

When Jesus asks the question, there's no indication that the phrase "I am" here means He is claiming to be the I AM, as used in Exodus 3:14 or as repeated in the Gospel of John. In John 8:56–59, Jesus tells the Pharisees, "Before Abraham was, I am," and the Pharisees know immediately Jesus is claiming to be God. Again, at the garden of Gethsemane, when the chief priests and Pharisees ask if He is Jesus of Nazareth, He responds, "I am he." Those words hold such power the men fall to the ground (John 18:3–6). Here, however, He is just asking a question.

The Socratic method of teaching uses questions and answers to help students think through the possibilities and derive the answer on their own. By asking the disciples first who others think He is (Mark 8:27), He gives them space to consider what they have heard. Then, by asking what they think, He allows them to consider the evidence for themselves. Instead of having to come up with their conclusion on the spot, they are able to first determine if the other claims fit with what they've seen and heard. With the alternatives considered and discarded, the only remaining option is that Jesus is the Christ.

"Christ" is from the Greek root word christos and means anointed. In Hebrew, it is "Messiah." Luke's version says, "the Christ of God" (Luke 9:20); Matthew 16:16 says, "the Christ, the Son of the living God." Mark, as he often does, condenses the statement. Peter is given the honor of finally answering the question the Twelve had posed after they witnessed Jesus calming the storm: "Who then is this?" (Mark 4:41). Before too long, however, Peter will deny even knowing Jesus (Mark 14:66–72).