Andy Bryan has written two posts (hat tip) about how American Christians in general and Methodists (in reflection of our Social Principles) in particular should respond to illegal immigration and calls for reform.
As he says, the Bible seems fairly clear that the policy guidelines outlines by God for the Israelite state included generosity toward immigrants, especially since such foreigners could not own land and as a consequence, would likely be impoverished.
I am unsure if these features of Mosaic Law were intended only for the Israelites at the time or can and should be followed by all citizens of all future states that ascribe to worship Yahweh. One must be careful applying laws for the Israelites to modern times, lest you find yourself stoning homosexuals to death on an otherwise pleasant afternoon.
The New Testament has nothing specific to say about immigration policy, or political policies at all, since the Gospel is clearly presented as a transnational message.
That said, I think that a Christian response to immigration policy is part of the larger issue of the relationship between and within the individual Christian and the role of the state. For example, can a Christian use violence in the defense of his state against invasion? Can he kill for his country and remain a faithful Christian. I have no resolution to this issue, but my default position (until such time as I can find a solution) is 'yes'.
In the same respect, can a nation defend itself from an immigration invasion? Can Christians advocate laws to provide for the integrity of its borders? Again, there is muddling on this issue, so until resolution, I say 'yes'.
So I don't know about how to apply Christian ethics to national immigration policy, but on the political level, I think that the problem is pretty clear: we are facing the dissolution of the United States culturally and politically.
I really enjoy being in the dominant, majority culture. While my ancestors may have worn kilts and lederhosen and spoken Gaelic and German, upon arrival they soon dropped these identities and joined the dominant national culture of the United States, which is English-speaking and Protestant (literally or effectively) along with various other attributes that make American culture American. The experience of my ancestors is a common one, as immigrants rapidly assimilated into the dominant culture, whose descendants today have no real ties to their ancient homelands.
That dominant culture is being washed away in favor of a different one from Latin America. The new wave of immigrants have little to no desire to assimilate to the dominant culture. In fact, they are becoming the dominant culture. That bothers me because I like my culture and I don't want to see it go away. Many Americans agreed in the past, which is why immigration policies a century ago advocated assimilation, and largely succeeded. We made a deal with immigrants: you can come to our country, but you have to join our culture. As an independent polity, I think that we have inherent property rights to our own territory and can therefore require such bargains. No one has a right to come to our country anymore than anyone has a right to walk into your house and start living there.
But beyond our lovely culture being absorbed into a different one, we Americans also face a real political danger from massive immigration from Latin America. Healthy states are ones that are largely uniform. Although multiethnic societies can thrive, multicultural societies fail, almost without exception, such as the Soviet Union and Yugoslavia (which don't exist anymore. Guess why). Multiple divergent cultures within one polity ultimately lead to Balkinization, a process exacerbated if those divergent cultures actually have different languages. If people can't even talk to each other easily, they have trouble forming a cohesive society.
In America, this problem is seen in a large Mexican population which identifies with Mexico, has no plans to join the dominant culture, has less motivation to learn English, and sees the land that it populates as stolen from their homeland. In spite of efforts by critics to tie these fears into historical nativism, Americans have real reasons to worry, as Jonah Goldberg writes:
Obviously, there's some truth to this. Many of the complaints do sound similar. But that doesn't mean the arguments have the same weight. The arguments against interracial marriage sound very similar to the arguments against gay marriage, but that doesn't mean a black woman marrying a white man is the same thing as a man marrying another man.
Similarly, people may have complained about the ability of legal immigrants from Italy to assimilate, or fretted that these Italian immigrants were taking jobs from Americans, but that doesn't mean illegal Mexican immigrants in the early 21st century are indistinguishable from legal Italian ones a century ago. The fact is that America has never shared an enormous border with Italy. Large chunks of U.S. soil never belonged to Italy or Ireland. You can be as romantic as you like about the glory and honor of America's noble tradition of accepting the "wretched refuse" of the world: It won't change this very basic fact.
We are looking toward a future in which the majority of the American Southwest speaks only Spanish, has no ties to the traditional culture of the United States, and no plans to acquire them. They will not identify with the United States, and while for economic reasons they are unlikely to secede and join Mexico, the fact that they would have the capacity to do so should worry us. Last weekend, 500,000 illegal immigrants demonstrated in Los Angeles, along with other large rallies across the country. Many waved Mexican flags and said that they considered the land on which they were standing to be stolen from their homeland. That's called a 'clue': they don't consider themselves to be a part of America.
So culturally and politically, let's do the smart thing: drive the illegal aliens out, keep them out, and wait a couple generations for the Mexican population here legally to be absorbed into our culture before resuming large-scale immigration from Mexico.
UPDATE: Joe Cathey has a few practical suggestions for reforming our immigration policy. Richard Heyduck thinks that we should take a more organic view of immigration.