Here’s a great article from Tim Stratton writing for Cross Examined on the subject of politics and religion. It isn’t very long and I recommend reading the whole thing (links removed):

If God exists and Christianity is true, however, then one’s subjective political opinions can be objectively right or objectively wrong.
…
First, consider the fact that Jesus constantly interacted with the Pharisees in the New Testament. The Pharisees were the religious and political rulers of Israel. Matthew 23: 23-24 provides a good example.
…
Think about the “more important matters of the law” and modern-day America. Politicians today are more concerned about the consequences of using plastic drinking straws than placing restrictions on abortion (killing innocent human beings) and actually advocate for it in many cases. What do you think Jesus would say to these politicians? Based on His reaction to the political leaders of Israel, do you think Jesus would worry about hurting the feelings of modern-day politicians or those who vote for them? We must not disregard the “more important matters of the law.”
…
Second, if a Christian does not take politics seriously, then they probably do not take evangelism seriously. Frank Turek shows a satellite image of the Korean peninsula to make this point (See Why Christians Should Be Involved In Politics).
…
Notice the stark contrast between the north and south. South Korea is filled with light, activity, and productivity. According to Turek, “it is one of the most Christianized countries in the world.” North Korea, on the other hand, stands in polar contrast to their neighbors south of the border. North Korea is dark and seemingly “dead.” Turek accurately describes it as a big “concentration camp.” What is the difference between North and South Korea? One word: POLITICS!

Many South Koreans have heard the gospel of Jesus Christ because there is political freedom to share the gospel. The communistic government of North Korea, on the other hand, does not allow the gospel to be shared — it is a dictatorship. If you are a Christian, Sean, then you know that the gospel message is the most important information a person could ever have access to or possess. If you truly love all people — as Jesus commanded — then you must desire the people who have never heard the gospel to have access to this eternally vital information. Since politics is keeping millions of souls from hearing the gospel, if you truly love and care for all humans, then you should care about politics.

He goes on to write about the fact that every single election and political decision is a choice between the lesser of two evils. On Earth, that’s the only sort of political decision we can make.

I think it’s not only wise for Christians to do more than have private piety, but commanded. Christianity is not a private religion for us to have spiritual experiences. It’s a worldview. It touches every aspect of human life. True enough, it is not like Islam, which specifically prescribes clothing, music, forms of government, festival schedules, dietary laws, etc. Christianity is the true worldview, not the true legal code. But that doesn’t mean Christians must avoid public life. On the contrary, it means Christians need to not only engage in public life, but need to be wise and thoughtful in how they do it. Christians aren’t given a form of government like Islam to impose on the world. Rather we need to reason about what form of government might be best at any particular place and time.

Many Christians think it is somehow more obedient, pious, or spiritual to avoid getting religion and politics tangled up. I suggest that it’s impossible to do that. The alternative to letting your Christian worldview influence and guide your political philosophy is to let some other worldview influence and guide your political philosophy. When I see Christians choosing a different worldview, it invariably turns out to be a form of whatever is popular at the moment.

I think this reasoning helps explain the phenomenon at The Gospel Coalition, Christianity Today, many seminaries, popular Christian music groups, etc. The trend is towards secular humanism, cultural Marxism, and radical liberalism. Those happen to define the popular worldview at the moment, and so those groups and organizations which refuse to intentionally form their political philosophy in light of their Christian worldview pick up those things instead.

For more on the subject of the sacred/secular divide, I recommend Nancy Pearcy’s “Total Truth”.