The Bible shows believers as holding important posts in pagan governments -- think of Joseph and Daniel in the Old Testament. Christians should be involved politically as a way of loving our neighbors, whether they believe as we do or not. To work for better public schools or for a justice system not weighted against the poor or to end racial segregation requires political engagement. Christians have done these things in the past and should continue to do so.

Nevertheless, while believers can register under a party affiliation and be active in politics, they should not identify the Christian church or faith with a political party as the only Christian one. There are a number of reasons to insist on this.

One is that it gives those considering the Christian faith the strong impression that to be converted, they need not only to believe in Jesus but also to become members of the (fill in the blank) Party. It confirms what many skeptics want to believe about religion -- that it is merely one more voting bloc aiming for power.

Another reason not to align the Christian faith with one party is that most political positions are not matters of biblical command but of practical wisdom. This does not mean that the church can never speak on social, economic and political realities, because the Bible often does. Racism is a sin, violating the second of the two great commandments of Jesus, to "love your neighbor." The biblical commands to lift up the poor and to defend the rights of the oppressed are moral imperatives for believers. For individual Christians to speak out against egregious violations of these moral requirements is not optional.

However, there are many possible ways to help the poor. Should we shrink government and let private capital markets allocate resources, or should we expand the government and give the state more of the power to redistribute wealth? Or is the right path one of the many possibilities in between? The Bible does not give exact answers to these questions for every time, place and culture.

I know of a man from Mississippi who was a conservative Republican and a traditional Presbyterian. He visited the Scottish Highlands and found the churches there as strict and as orthodox as he had hoped. No one so much as turned on a television on a Sunday. Everyone memorized catechisms and Scripture. But one day he discovered that the Scottish Christian friends he admired were (in his view) socialists. Their understanding of government economic policy and the state's responsibilities was by his lights very left-wing, yet also grounded in their Christian convictions. He returned to the United States not more politically liberal but, in his words, "humbled and chastened." He realized that thoughtful Christians, all trying to obey God's call, could reasonably appear at different places on the political spectrum, with loyalties to different political strategies.

Another reason Christians these days cannot allow the church to be fully identified with any particular party is the problem of what the British ethicist James Mumford calls "package-deal ethics." Increasingly, political parties insist that you cannot work on one issue with them if you don't embrace all of their approved positions.

This emphasis on package deals puts pressure on Christians in politics. For example, following both the Bible and the early church, Christians should be committed to racial justice and the poor, but also to the understanding that sex is only for marriage and for nurturing family. One of those views seems liberal and the other looks oppressively conservative. The historical Christian positions on social issues do not fit into contemporary political alignments.

So Christians are pushed toward two main options. One is to withdraw and try to be apolitical. The second is to assimilate and fully adopt one party's whole package in order to have your place at the table. Neither of these options is valid. In the Good Samaritan parable told in the Gospel of Luke, Jesus points us to a man risking his life to give material help to someone of a different race and religion. Jesus forbids us to withhold help from our neighbors, and this will inevitably require that we participate in political processes. If we experience exclusion and even persecution for doing so, we are assured that God is with us (Matthew 5:10-11) and that some will still see our "good deeds and glorify God" (1 Peter 2:11-12). If we are only offensive or only attractive to the world and not both, we can be sure we are failing to live as we ought.

The Gospel gives us the resources to love people who reject both our beliefs and us personally. Christians should think of how God rescued them. He did it not by taking power but by coming to earth, losing glory and power, serving and dying on a cross. How did Jesus save? Not with a sword but with nails in his hands.

Timothy Keller, founder of the Redeemer Presbyterian churches in New York City, is the author of "Prodigal Prophet: Jonah and the Mystery of God's Mercy," from which this essay is adapted.
Follow The New York Times Opinion section on Facebook and Twitter (@NYTopinion), and sign up for the Opinion Today newsletter.