(paraphrasing from the Ignatius study Bible)
It’s about loving your enemies and not seeking personal revenge.
If someone (like a Roman) took their cloak (outer garment), they would not refuse to be robbed of their coat (inner garment) as well. In the face of oppression, Christ’s followers must not seek retaliation, even under personal abuse and mistreatment, allowing themselves to suffer as Christ did, for His sake.
32 But recall the former days when, after you were enlightened, you endured a hard struggle with sufferings, 33 sometimes being publicly exposed to reproach and affliction, and sometimes being partners with those so treated. 34 For you had compassion on those in prison, and you joyfully accepted the plundering of your property, since you knew that you yourselves had a better possession and an abiding one. Heb 10:32-34
See also 1 Cor 6:1-7 about not going to the law to seek retribution.
Also, remember how it relates to the Sermon on the Mount.
Blessed are those who are persecuted for righteousness’ sake, for theirs is the kingdom of heaven.
Blessed are you when others revile you and persecute you and utter all kinds of evil against you falsely on my account.
Rejoice and be glad, for your reward is great in heaven, for so they persecuted the prophets who were before you. Matt 5:10-12