He who has suffered in his body is done with sin

1 Peter 4:1-6
Because he who has suffered in his body is done with sin. As a result, he does not live the rest of his earthly life for evil human desires, but rather for the will of God. -- Benefit of suffering
They will have to give account to him who is ready to judge the living and the dead.
They might be judged according to men in regard to the body, but live according to God in regard to the spirit.
Peter anticipates a time of suffering and persecution for his readers.
Why?
Peter is talking about those who suffer for doing right, not sufferers in general.
Christians who are now dead. They suffered the judgment of death, like other people, but they will live.
If we suffered in body for we doing right, let us do not live the rest of earthly life for evil human desires, the faith is strengthened.
Christian will die to the body, but live according to God in regard to the spirit. It is the eternal life.
Suffering always has close relation with sin. No matter against sin or follow the desires of sin. But it is always again the flesh and most earthly people.
How?
Suffered for the right is worthy, do not fear or worry about what we will face, for God is always with us.