Jesus tells the person whose tunic is being claimed to surrender the outer cloak as well. The two garments were not interchangeable pieces of clothing.
Jesus in Context
Tunics, Cloaks, and a Debtor's Outer Garment
Jesus distinguishes the inner tunic from the more substantial outer cloak, a garment protected by biblical law when taken as security for debt.
Introduction
Historical and Cultural Context
The chiton was an inner garment or tunic, while the himation was an outer cloak or mantle. The outer garment could also serve as a covering during sleep. Exodus and Deuteronomy therefore required a creditor who took such a garment as security from a poor debtor to return it by sunset.
Why It Matters
The distinction makes Jesus' illustration more concrete. He describes voluntarily surrendering something particularly useful and legally protected rather than simply handing over a second equivalent garment.