Enemies

In Matthew 5:41, why did Jesus suggest that if a soldier from enemy occupation forces asks us for help carrying their equipment a mile, we should carry it two? In Roman occupied Palestine, there was a law that if a Roman soldier asked any Jew for help, they were required to come to their aid. Jesus alluded to just such a scenario where it was common for an enemy soldier to ask a Jew to carry arms for a distance. Jesus suggested helping out to double the distance asked. Jesus challenges us by teaching what is the exact opposite of our natural inclination. God is impartial and treats all people equally. Do we?