I can't emphasize enough the importance of today's gospel pericope. It not only sets the theme for Mark's entire gospel, it also gives us an insight into the historical Jesus' ministry.
Though I, like most of you, was taught the reason Jesus, the second person of the Trinity, came to earth was to show us the way to heaven, this passage points us in a somewhat different direction.
There's some "unease" with this "get-us-into-heaven" theology among those who read Mark's gospel carefully, especially because of chapter 10's rich young man narrative. Notice what he asks Jesus: "Good teacher, what must I do to inherit eternal life?" In other words, "What will get me into heaven?" Jesus responses, "Keep the commandments." When he assures the teacher that he's kept them from his youth, we presume he's eventually going to get into heaven. So when Jesus tells him there's something he's still lacking, the missing element has nothing to do with the man's eternal happiness. This is verified when Jesus later observes, "How hard it is for those who have wealth to enter the kingdom of God." For Jesus, entering heaven and entering the kingdom of God are obviously two different states of life.
That's why our gospel pericope is so important. It not only contains the first words of Jesus' public ministry, we presume he includes these words in every sermon, instruction, and homily he delivers during that ministry. They're an essential part of his "stump speech." "This is the time of fulfillment," he announces. "The kingdom of God is at hand. Repent, and believe in the good news!"
Scholars tell us the phrase "kingdom of God" (or "kingdom of heaven" in Matthew) doesn't refer to the place we plan to inhabit after our physical death. It refers to God working effectively in our lives right here and now. That's the "good news" Jesus spends his ministry proclaiming, and for which he'll eventually be crucified. In the rich young man narrative, he seems to presume people can "get into heaven" without entering the kingdom of God. He shutters his Capernaum carpenter shop and goes village to village, synagogue to synagogue encouraging people to experience God in their lives long before they leave this life.
There's just one kicker: Jesus is convinced that in order to experience God they must "repent." The Greek word employed here - "metanoia" - implies more than just "I'm sorry I did it; and I won't do it anymore." In this context, repent refers to a total change in one's value system: a one hundred and eighty degree shift in what one holds to be important in his or her life. Mark will spend the rest of his gospel informing us of the characteristics of that shift.
It now makes sense why the rich young man walked away from Jesus' invitation. Repentance for him entailed concentrating on people instead of making money; a step lots of rich individuals find impossible to take. They'd be forced to develop a completely different lifestyle.
That's why baptism by immersion was such a meaningful sign for Jesus' first followers. As the author of I Peter puts it, it's more than just "a removal of dirt from the body." It's a dying and rising entrance into a whole new life.
Early Christian authors often used the flood as a symbol of the life they were now living. Just as the original Genesis flood survivors entered a new relationship with Yahweh, so we who have "survived" the waters of baptism enter a new relationship with God.
If we spent less time worrying about getting into heaven, and more time concentrating on what's necessary to surface God here and now, perhaps we'd eventually become the other Christs Jesus intends us to become.