President Obama is pivoting once again to decrying the alleged sin of income inequality -- the left's perennial and favorite class-warfare theme. At the same time, the religious left is becoming more vocal in American politics, couching its opposition to income inequality in theological rhetoric. When Rush Limbaugh and Sarah Palin took shots at Pope Francis for his apparent critique of capitalism, leftist religious scholar Reza Aslan pounced. Writing in The Washington Post's "On Faith" section, Mr. Aslan contends that Jesus preached "revolutionary social teachings" whereby "the rich will be made poor, the strong will become weak, and the powerful...