Context of Mark 8:31 and following, the 2nd half of Mark's Gospel

Most scholars regard verse 31 of Mark 8 as the second half of Mark's gospel.
Mark's primary, though not exclusive, concern in the first half was to answer the
question, "Who is Jesus?" Peter's confession, "You are the Christ" brought this
section to it's climax.
The chief concern in the second half of the Mark's gospel is to answer the
question, "What did Jesus come to do?" What is partially answered now
becomes explicit: He has come to die for our sin and be raised from the dead so
that we might experience redemption. The second half also deals more explicitly
with the question, "What does it mean to follow Jesus."
Jesus' death becomes the paradigm upon which Christian discipleship is based
("deny yourself and take up the cross"). It is the central metaphor for what it
means to follow him. This passage (8:31-9:1) is part of a fairly distinct section of
Mark's gospel that extends from 8:31-10:52. "The primary purpose of this
section is to explain what it means for Jesus to be the Messiah and what it
requires to be identified with him."
Throughout these chapters Jesus and the disciples are on their way to Jerusalem.
This destination is finally announced in Mark 10:32ff. Therefore, while Mark is
telling us what Jesus' mission is in these chapters, we are being led closer to
Jerusalem where his mission will be accomplished. Mark 8:31-9:1 is to Mark part
II what 1:14,15 was to Mark part I: a summary proclamation about Christ and
demand for a response which is then expanded on in the chapters which follow.

--from Redeemer Presbyterian Church in NYC, i think jeff white wrote it