3/6  .... Rather, Jesus zeroes in on our actions and attitudes toward others. He offers no platitudes about how outsiders should be viewed. .... The exhortation is underlined by three concrete examples. First, if someone strikes you on the cheek, then offer him the other. Probably, given the context of religious persecution, the slap refers to exclusion from the synagogue. .... Second, Jesus gives the example of someone stealing one's outer garment. He advises letting them have the undershirt too! The point is that one should not seek revenge but remain exposed and be willing to take even more risks.”  - IVP New Testament Commentary

This exhortation deals with one-on-one relationships on the part of the disciples as themselves. It does not address the disciples as citizens of a state, which He already addressed with his “Render to Caesar” admonition.