It took Lisa Sharon Harper nearly 10 years to reconcile her faith with her political views. Then she met her first self-described evangelical Democrat in 1991.

At the Los Angeles Nazarene congregation where she attended after college, about half the members were Republican and half were Democrat. It was the first time Harper realized she could both serve God and stay true to her family and upbringing.

Harper, recently named the director of mobilizing at Jim Wallis's Sojourners, was raised by politically involved parents who had her knocking on doors to get out the vote as early as age 7. In a new book, she says she views politics primarily through the impact of policies on relationships, corresponding to the way she understands God's relational view of his creation.

The book, Left, Right & Christ: Evangelical Faith in Politics, released last month from Russell Media, confronts conflicts that fellow believers face over policy and politics. Harper unabashedly represents the Left, while King's College politics professor D. C. Innes represents the Right.

Harper calls the book "a tool to help more Christians be involved in politics." She and Innes agree that "political disengagement is not a moral option." But while both writers are self-avowed Christians, neither pulls any punches about having nearly completely opposite political positions.

"We wrote it in order to give Christians the ability and permission to think, especially evangelicals, because over the past 30 to 40 years or so we've really been trapped in ideologies and the belief that we can't be Christians without being in one party who cares about one or two issues," Harper told me.

Co-author Innes told me the book should encourage believers to think about the principles behind the policies. "You have to decide principles before you can decide practice," he said.

The book is not a defense of Christians who lean left—or vice versa. "It's not 'Republican, Democrat and Christ,' " Harper said. "[The title] does set up a political spectrum, but it's actually not about the parties. It's actually about the worldview."

Harper and Innes don't agree on much policy, but the book stresses that it is possible to disagree on almost everything else and still agree that God is God—and that self-identifying as a Democrat or Republican before identifying as a Christian is idolatry.

Harper and Innes said they are both registered with the respective parties because their faith-filled policy positions most closely line up that way.

"I am a Democrat, but what I would say is, I am a Democrat in as much as the Democratic Party is pressing for policies that do justice," Harper said.

"The parties don't line up as Christian parties," Innes similarly noted, suggesting that a Christian's positions likely will and should differ from the party she or he most closely aligns with at some point or another.

Innes notes a tension in acknowledging that believers aren't always united behind the same policies or party. "If there is only one position, there isn't much thought about that position," Innes said.

Still, the political differences as laid out in the book betray a commitment to the principles of the two parties' platforms.

For example, Innes argues that the Bible advocates for less government interference. "God appoints government for our benefit, but it is not to provide every good," he writes in the book. "Rather, government is to encourage private citizens, communities, and citizen groups to address the many needs that arise among us, from beautification projects to helping the poor, the sick, and the homeless."

Harper, on the other hand, argues that the big vs. small concept is a "straw man" argument. "The real issue is whether you have smart government or ineffective government," she said.

Harper, who now attends an Evangelical Covenant church in New York City, relates her work at Sojourners to her understanding of God's definition of "good" in Genesis. She writes that in Hebrew, "good" defined the relationships between every possible thing, not just creation itself.

The two authors had never met before publisher Russell Media set them up for the book, which includes two points of view on six topics: health care, abortion, same-sex marriage, immigration, war and terrorism, and the environment.

On abortion, likely the widest gap between the two parties' positions, both authors define themselves as pro-life.

Harper emphasizes poverty as the root cause of high abortion rates. "We absolutely can agree that babies are among the least of these, but they are among the least of these, they are not the only ones," Harper said. "To measure vulnerability, to say one is more vulnerable than the other, it feels like a political ploy." In the book, she also argues that government in a pluralistic society cannot define life according to "the specific mandates of the Christian faith."

Innes disagreed, arguing that poverty and abortion should be addressed separately just as we would high rates of murder in a poverty-stricken neighborhood. "The unborn children are not one among the least of these," he said. "They are the absolutely helpless. Even the poor among us … have some means to defend themselves." He added that one of the primary obligations of government is to protect the defenseless.

Left, Right and Christ is not likely to convert anybody who takes a position on hot-button policies. But it is a reminder that when it comes to politics, the party shouldn't call the shots.