“Going the extra mile” was a rare term originally used for the stages ridden by officers in the Persian postal service, but in first-century Palestine referring especially to the Roman soldier’s right to enlist a member of the subject population for forced labour, in this case presumably as a porter for his equipment; the only other NT use of the verb is for Simon of Cyrene forced to carry Jesus’ cross (27:32). This oppressive practice was of course deeply resented by the people of occupied Palestine, but it was a Roman legal provision and they would have no choice about complying up to the limit required (“mile” was a Roman, not a Jewish measure). But Jesus calls on the disciple not only to accept the imposition but also to volunteer for a double stint. To do this for anyone would be remarkable, but to do it for the enemy was unheard of. This cameo thus serves not only to illustrate Jesus’ demand to renounce one’s rights, but also prepares us for his equally revolutionary command to love one’s enemies (v. 44), and suggests that Jesus advocated a response to the Roman occupation which not only full-blown Zealots but even the ordinarily patriotic populace would have found incomprehensible.
R. T France, The Gospel of Matthew