Some overdo Jesus’ being our example and end up converting all kinds of passages in the NT as examples — like going into a mountain anticipating a transfiguration, and others underdo it — like missing all sorts of opportunities to see the life of Jesus as one big recapitulation of human life. Peter strikes a balance, and in 4:1-6 presses home once again that Jesus is our example and more.
Peter finds a resting place for his suffering, Gentile, powerless Christian churches: the example of Jesus. “Arm yourselves with the same understanding.” Let’s begin with this observation: this isn’t cute. There is nothing simplistic, but everything hard-earned; there is nothing shallow, but everything penetrating in this passage. To summons a group of folks, a first generation group of Christians, the first in Asia Minor, and the first to be rendered powerless and in danger of death — to summons this group to find in Jesus a good example is nothing less than to urge them to be ready to pick up the cross. He becomes their exemplar, as he was in chp. 2.

Why? Peter is working here to find answers for pressing problems, some of them new. His theology is emerging: Why should we follow Jesus, he thinks to himself, to the cross? 4:1-2 is not easy to interpret — “whoever has suffered in the flesh has ceased from sin” — but the first reason seems to be this: because suffering is a tough taskmaster, but it clearly teaches that sin is not worth its own pleasures. Suffering disciplines the body and teaches it not to sin. They’ve suffered; they’ve learned the impact of suffering on its disciplining powers, and therefore they need not sin.
A second reason: Peter tells them they’ve already sinned enough. (I think this text indicates clearly that Peter’s readers are Gentiles.) Rather obviously, this is a pragmatic argument, or a commonsensical argument, and it does not get developed enough for us to know with any clarity where it might lead for Peter. Letters written like this have just that sort of less than complete development. But, the argument works for many: those who have lived a life of sin and who have found redemption know they don’t want to return to that again.
And a third reason: the final judgment. Peter summons his churches to avoid sin, following in the path of Christ, and part of his reason for that summons is because they (and everyone else) will have to give an account (roughly the same as 3:15) to the One who judges both the living and the dead.
And now Peter brings us right back to Jesus: just as Jesus was put to death in the flesh and made alive in the spirit (3:18), so the Christians of Asia Minor need to know the implication of that death/made alive: “the gospel is preached to the (now?) dead, so that they can be judged by men in the body but live before God in the spirit.” Hard to know what to make of this: my own thinking is the “dead” are those who heard the gospel but were judged (put to death/suffered) in their body but who, nonetheless, live before God. In other words, Jesus is their path-breaker and leader through this life into the life with God.