1 Peter 4:1-2

1 Therefore, since Christ suffered for us in the flesh, arm yourselves also with the same mind, for he who has suffered in the flesh has ceased from sin,

² that he no longer should live the rest of his time in the flesh for the lusts of men, but for the will of God.

In 3:18-22 Peter spoke of the sufferings of the Lord Jesus and of His example of patience and submissiveness under unjust treatment. Now, he exhorts the saints to arm themselves with the same mind that Christ had regarding unjust punishment. Our Lord’s attitude toward unjust suffering is found in the words, “It is better, if the will of God be so, that ye suffer for well doing, than for evil doing” (3:17). The Greek word translated “arm yourselves” was used of a Greek soldier putting on his armor and taking his weapons. … The Christian needs the heaviest armor he can get to withstand the attacks of the enemy of his soul. To have the same attitude toward unjust suffering that the Lord Jesus had, will cause us to react toward this suffering as He did. — Wuest, page 110

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The fact that he has been persecuted is an indication … that he has ceased from sin. The world directs its persecution against those who are living lives of obedience to God, thus those who have ceased from sin. The verb is passive. Literally, the Christian “hath got release” from sin. God broke the power of sin in his life when He saved him. Thus our reaction to unjust suffering should be that of a saint, not a sinner, since we have in salvation been released from sin’s compelling power. — Wuest, page 111

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The added argument here [in addition to the point of the last verses of chapter 3] is that suffering is better than sinning. To be exempted from suffering is desirable, but to be saved from sinning is much more desirable. … To “suffer in the flesh” means to be put to death (v.1). To arm oneself with the same mind is to reckon oneself to be dead (Romans 6:11). Death is an effective breach with sinning; for how can a dead man practice sinful passions (v.2)? A living man, raised with Christ, lives to do the will of God. — Williams, page 1002.

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Why do we suffer? the answer to this question has been a matter of debate since the days of Job. Usually the sorrows of man are a product of his own sinful behavior. But God often has a purpose in suffering. The fact that Christ came into the world to obey the will of His Father is indisputable. Even though the Savior was unjustly treated, He purposed in His heart that He would suffer and die at the hands of evil man before he would ever disobey the will of the Father.

Thus, Peter gives this admonition, “arm yourselves likewise with the same mind.” Like the mighty man of war who takes up a shield to defend himself, Peter’s hearers were to arm themselves with the same attitude as the Savior. That is, they were to be obedient to the will of the Father.  As we know, the world has a special hatred for those who obey the will of God, thus these saints were suffering because they had “ceased from sin.” They were dead to sin, therefore, they refused to allow it to control their lives. …

Peter wanted his countrymen to be fully aware that they only had one lifetime to serve the Lord. Those years and opportunities that were lost could never be recovered. However, it was in their interest to use “the rest of the time” they had remaining to carry out the counsel of His will. The sufferings and hardships they would endure as a result were not to be compared with the glory they will receive in the coming kingdom (1 Peter 1:7 cf. 2 Peter 1:11). — Sadler, pages 131-132.