Our translation makes the link with the use of the connective word “for.” That would suggest that with the words of the second part of the verse (“whoever has suffered…has ceased from sin”), Peter is providing the reason why his readers need to arm themselves: “because whoever has suffered…” The Greek term Peter uses, however, can also be translated as “that,” so that the whole sentence would read: “with the same way of thinking, [namely], that whoever has suffered….” In the latter case, the second part of the verse is descriptive of what “the same way of thinking” is (or better, the result of that way of thinking). Christ’s mindset as he suffered abuse was to entrust himself to the righteous Judge (1 Peter 2:23), convinced that God would vindicate him publicly in due time, and so Jesus was done with sin, had no appetite to sin as a method to escape suffering. With his resurrection, ascension, and enthronement God did publicly vindicate Jesus. That fact is reassuring for suffering Christians; God in his time will also vindicate them.
1 Since therefore Christ suffered in the flesh, arm yourselves with the same way of thinking, for whoever has suffered in the flesh has ceased from sin,