The second part of Matthew 5:38-42 talks about given one’s cloak to the guy who takes your tunic:
And if someone wants to sue you and take your tunic, let him have your cloak as well.
Giving Up Your Cloak: A Cultural View
Back in the day, the poor could get a money loan by giving up their tunic as collateral. One of the guide lines for such a loan in the Mosaic law said that the person giving the loan must return the loaner’s tunic each evening. These was because the tunic was used as a blanket during the night.
Now in Matthew 5, Jesus is speaking to mostly poor people – who where generally being oppressed by the rich. By telling the poor to give up their cloak (or underwear) as well as their tunic, Jesus was starting a civil rights movement.
Now the poor would be running around naked, officially shaming those who opposed them for their financial gain.
Are you starting to see a trend? It wasn’t like Jesus was telling the poor to role over and play dead. He was starting a nonviolent resistance movement!!!