Moses did not in person lead the war against Midian, for he was mindful of the proverb, "Cast no stone into the well from which thou hast drawn water," and he who as a fugitive from Egypt had sought refuge in Midian, did not wish to make war upon that land. He relinquished the leadership of the people to Phinehas, for "he that beginneth a good deed shall also complete it," and it was Phinehas who had begun God's war against the Midianites by slaying the princess Cozbi, Zimri's mistress, hence the task of completing this war fell to his lot. Phinehas, as a descendant of Joseph, had, moreover, a special reason for wishing to take revenge upon the Midianites, as those had been Midianites who had sold Joseph as a slave in Egypt.