“Watu Wote” shows the power and limits of African and Arab films to probe interfaith relations. Two years ago, the heroic actions of some Kenyan Muslims brought their majority-Christian nation together. The Oscar-nominated film depiction of that heroism may do so again—if many people watch. Watu Wote is a fictional retelling of real-life horror. In December 2015, al-Shabaab terrorists stormed a bus headed toward the border with Somalia and demanded Christian passengers separate for targeted execution. Muslim passengers responded, “If you want to kill us, then kill us. There are no Christians here.” The Christian women were given hijabs to…