These days no one really knows how or why the Magen David (the Shield of David) with its 6 pointed star became the official symbol of Judaism, but story has it that the Star was emblazoned on the Shield that David, the future King of Israel, used when, as a boy,  he went up against the giant Goliath on the battlefield in the Valley Elah.  But, everyone who knows that story also knows that David defeated the Giant with no protection–he just had his sling shot and his faith.