The lectionary went with a passage from John for this Sunday, so here’s a bit from Loosing the Lion on Mark’s Theology of the Cross:
The root of the sacrifice of the Eucharist is Jesus’s sacrifice on the Cross, which the Eucharist interprets and from which the Eucharist flows, and indeed, the theme of the Cross is central in Mark’s story. Jesus declares at Caesarea Philippi that “it is necessary” (dei) for him as Son of man to “suffer many things, and be rejected by the elders and the chief priests and the scribes, and be killed, and after three days rise again” (8:31). And then, in the Cross, we find the essence of discipleship. Jesus calls those who would be his disciples to come to Jerusalem with him to suffer crucifixion: “If any man would come after me, let him deny himself and take up his cross and follow me” (8:34). Like the master, so the disciple; discipleship is cruciform.
That’s why Peter freaks out and rebukes Jesus (8:32). He can’t countenance a crucified Christ. (In his defense, Peter was a Jew and Jews simply didn’t have a category for a crucified Christ; it’s like a square circle or a feline canine. But he failed to submit, forgetting that Jesus the Christ is the one who gets to define what all things ultimately mean.) But Jesus ups the ante: not only must the Christ suffer and die, but if one wants to be a disciple, one must “follow” him “on the way” to Jerusalem, to go and die likewise. In the world of the story, it’s a literal call to crucifixion. Allegorically, it’s a call to spiritual mortification—and, for too many Christians in the wider world today, martyrdom.
Indeed, again and again in Mark’s Gospel, one sees a contrast between a theologia gloriae and a theologia crucis, between a theology of glory and a theology of the Cross. Theologies of glory evade the Cross; they’re all gain, no pain, allergic to suffering. Theologies of the Cross recognize the depth of human sin revealed and conquered in the crucifixion, necessary for salvation. They recognize that Christianity is cruciform through and through, that suffering is redemptive.
The theology of glory is Peter’s problem at Caesarea Philippi: he assumes Christhood involves glory, and Jesus teaches it requires the Cross. In fact, it’s Peter’s problem at the Transfiguration, too. He’s overwhelmed by Jesus’s proleptic resurrection glory, but the heavenly voice reminds Peter that Jesus is God’s “beloved Son”—like Abraham’s beloved Son Isaac (see Gen 22:2, 12, 16), Jesus is meant to be a sacrifice. And Peter is not the only disciple captured by fantasies of glory. Immediately after Jesus’s final Passion prediction (10:32–24), Mark juxtaposes James’s and John’s jarring demand to sit at Jesus’s right and left hands “in [his] glory” (10:37). It’s as if their theology of glory blinded them to Jesus’s theology the Cross. Thankfully, Mark’s Gospel teaches there’s hope for the blind!