The trouble is that following the words of Jesus doesn’t necessarily lead to a specific or constant set of policy decisions. WWJD about universal pre-K and school-busing policies? The Keystone pipeline? China? There are always ways to draw wisdom from text, of course, and for Christians, this is particularly true of the Bible. But Rubio’s claim that he lives to follow God’s plan doesn't tell voters much about how he’d govern. Indeed, a lot of liberal Christians would claim that they, too, live their lives in the imitation of Christ, and also seek to follow God’s plan. It’s not clear whether living like Jesus is very much in keeping with either Democratic or Republican politics.
This might be a hint about what Rubio’s actually trying to do with this ad: nab the conservative voters who have gravitated toward other candidates. In many ways, evangelical Christians are becoming less intertwined with the Republican Party; the Southern Baptist leader Russell Moore has argued that the faith is making healthy moves away from the God-and-guns identity that was the lifeblood of GOP politics for so long. Nonetheless, Rubio may be betting that he can impress Christian voters with a strong declaration of faith. If he can show that his religious beliefs undergird everything he does, perhaps that will appeal to religiously conservative voters—to the point that they can overlook his moderate views on immigration, for example. Ted Cruz has regularly tried to portray Rubio as a moderate; this ad may be Rubio’s way of trying to show conservative voters that he’s just like them.
That theory also explains the curious idiom of faith used in the ad: Its language echoes common evangelical themes, which is ironic, because Rubio is a Catholic covert from Mormonism. “To accept the free gift of salvation offered to us by Jesus Christ—the struggle on a daily basis as a Christian is to remind ourselves of this,” he says. It’s not that Catholics don’t believe this. (Although, a free open-mic-night idea for Iowa: Republican candidates for president debate “faith, not works.”) It’s the tone, the open invocation of a direct relationship between a sinner and his God, that sets it apart. Arguably, Hispanic Catholicism tends to be a bit more charismatic than others strains of American Catholicism, and that may be sufficient explanation. But one could also argue that Rubio is trying to appeal to the quarter of Iowans who are evangelicals, a group that Cruz has assiduously courted in the lead-up to the caucus.
Of course, it’s always worthwhile to question how much of a unified bloc evangelicals and other religious groups actually are. Pollsters know certain things about their voting patterns over time, but it’s harder to know why, exactly, individual voters chose the candidates they did. Rubio may be hoping, though, that his faith will put him into consideration with Iowa voters as they try to pick their next president. It may be true that the daily struggle of Christians is to remind themselves of salvation. But the daily struggle of politicians, especially in this crowded Republican field, is to remind voters they exist.