It’s no surprise that major news networks, casting about for an expert on Christianity, would ring up Joel Osteen, senior pastor of the nation’s largest megachurch. The title “senior pastor” rests a little awkwardly on someone whose shiny, eager demeanor recalls a perpetual 20-something, but when duty calls Osteen can turn down the smile and look thoughtful. Last week’s duty was to appear on Wolf Blitzer’s Situation Room on CNN and answer Blitzer’s questions relating to Mitt Romney as the Republican candidate for president, including one asking Pastor Osteen how he would respond to a congregant who wants to vote for Romney but isn’t sure he’s a Christian.

Those are actually two different questions: Should a Christian vote for Romney? And are Mormons...