Adam Clarke on 1 Peter 4:1

As Christ hath suffered - He is your proper pattern; have the same disposition he had; the same forgiving spirit, with meekness, gentleness, and complete self-possession.

He that hath suffered in the flesh, hath ceased from sin - This is a general maxim, if understood literally: The man who suffers generally reflects on his ways, is humbled, fears approaching death, loathes himself because of his past iniquities, and ceases from them; for, in a state of suffering, the mind loses its relish for the sins of the flesh, because they are embittered to him through the apprehension which he has of death and judgment; and, on his application to God's mercy, he is delivered from his sin.

Some suppose the words are to be understood thus: "Those who have firmly resolved, if called to it, to suffer death rather than apostatize from Christianity, have consequently ceased from, or are delivered from, the sin of saving their lives at the expense of their faith." Others think that it is a parallel passage to Rom 6:7, and interpret it thus: "He that hath mortified the flesh, hath ceased from sin." Dr. Bentley applies the whole to our redemption by Christ: He that hath suffered in the flesh hath died for our sins. But this seems a very constrained sense.