The term “same” recalls Jesus Christ, which means that Peter here instructs his readers to copy Christ’s way of thinking.
The term translated as way of thinking
captures the mindset that drove Christ to persevere in the face of the abuse he received (whether the initial misunderstanding, or the later hatred, or the rejection and crucifixion). Peter had earlier alluded to that mindset or attitude or way of thinking when he wrote in 1 Peter 2:23 that Christ “continued entrusting himself to him who judges justly.” Now that Christ arose from the dead (1 Peter 3:18) and ascended into heaven (1 Peter 3:19, 1 Peter 3:22) and has angels and authorities and powers subject to him, Christians have great incentive to entrust themselves daily to the righteous judge (1 Peter 4:5). Injustice today will be set straight in the Lord's time, as also happened with Jesus Christ. That is the “way of thinking” we need to have straight in our minds.
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,