There is an old hymn entitled "Bless Be The Ties That Bind." The hymn talks about those things that Christians have in common. What is written in the hymn is important. But unfortunately, Christians can come away from singing that hymn with some wrong ideas.
The wrong ideas that many Christians have after singing "Bless Be The Ties That Bind" revolve around thinking that there are no significant ties between Christians and non-Christians--that is no ties outside of citizenship for patriotic Christians.
The result of this kind of thinking is that we have an Amish movement amongst some of my fine fellow flaming fundamentalists friends and family with the English of the world. To the Amish, the English are what the nations were to the Jews in Biblical times; that is you are in or your are out. You are either a part of the in group or you don't get it. And what we have is a sincere attempt, by many Christians, to be separate from the non-believers and even non-Christian fundamentalists of the world.
This separation though is not a physical separation simply because that would be impossible; rather, the separation is personal. In a very real sense, many Christian fundamentalists are refusing to be engaged with the world around them. Not that these Christians have grown tired of telling the world what to do, they haven't. But they have had it with reading, listening to and caring about those in the world, especially those who suffer in war zones. They have concluded that the world has nothing good to offer and so they have insulated themselves from the world with "Christian" topics and/or Christian sources. Some of these sources tell Christians that the solution is to take America back. But that back is a place that America never was in the first place.
Such Christians have little difficulty in finding scriptural justification for shunning the world's advice. For example, Paul tells us in II Corinthians 6:14, 17 that we should not bound together with unbelievers and that we should separate ourselves from them just as the OT Jews were called to come out from the Gentiles. These verses are tough to interpret because, at face value, they seem to imply that Christians should cut off all relationships with non-Christians. Thus it seems that a Christian would be obligated to leave a spouse if the spouse remained an unbeliever. And yet, Paul says the opposite in I Corinthians 7: 12-13. In addition, it is difficult for Christians to live amongst unbelievers without being connected.
And yet, these issues have not stopped many conservative Christians from trying to obey the II Corinthians passage by engaging in one-way relationships with non-Christians. These relationships consist of Christians feeling free to share their faith and expecting the non-Christian to listen while boldly asserting that the unbeliever has nothing worthwhile to say until they repent. The result is that the lives of some believers become islands as these Christians become more and more preoccupied with their own world. You can imagine how this could affect the carrying out of the Great Commission as more and more Christians tell the world that part of believing is to let the world crash and burn.
Is it true that the only ties a Christian has is with other Christians? Should Christians should separate themselves from the world as the Amish do from the English? Is there no common ground that the Christian and the unbeliever can share with each other that should move the Christian to listen to those outside of the faith and care about what is happening to others besides fellow Christians?
A variety of sources, both Biblical and others, says no! We could start with the liberal branch of Christianity which claims that all of us are the children of God and thus we are all brothers and sisters. The latter sentiment was expressed in a journal entry by Rachel Corrie when talking about the homeless. She said:
These are our brothers and sisters.
And that is what terrifies us.
They are us. And we could as easily be them.
The Christian fundamentalist balks at regarding everyone as a brother or sister and thus sometimes ignores the non-Christian who is in need. The titles of brother and sister, according to many conservative Christians, belong to fellow children of God only and with good reason. Nowhere in the New Testament do we read of anyone outside of the faith being called a brother or a sister. At best, non-Christians are called neighbors. We are told to love them as we would love those outside of the family. Thus there is a hierarchy in terms of whom the Christian should help. The Christian must help fellow believers first and then non-believers second. But with Christians turning their personal lives into islands and their churches into gated communities, the help that conservative Christians are giving non-Christians is shrinking fast except through the proxies called the missionaries.
Martin Luther King went beyond calling everyone his brother and sister as how he regarded the Vietnamese.  He called them God's children. That is what King called every person because each person is made in the image of God. He then concluded that what touches one touches all.  But is King justified in calling all people children of God? After all, not all people are fellow believers. In addition, Jesus called the religious leaders who rejected him children of the devil.
Adam is called a son of God(Luke 3:38). Why was that? In the third chapter of Luke, each person who was called the son of someone was a descendant of that person. Thus Adam, because he was both made directly by God and was made in God's image, was called a son of God. But note that the others were not called sons of God. They were merely called sons of their ancestors. Does that mean that Christians do not have to regard non-Christians as brothers and sisters? Is the closest tie that we Christians have with non-Christians is that of being a neighbor?
The answers to the last two questions are clearly NO! Since all people are said to be made in God's image, we can correctly regard everyone as a brother or sister regardless of their faith. These titles of brother and sister show a closer relationship that carries more grave results if we were to neglect those in need than if we just call people our neighbors. For to neglect someone in need who is made in the image of God shows an apathy or even hatred for God.
Having said this, Christians still need to distinguish between their brothers and sister by way of being made in God's image and their brothers and sisters by way of redemption. Much weight is put on Christians helping fellow Christians because Christ died for them. But our responsibilities to help fellow believers for whom Christ died do not eliminate the ties we have with nonbelievers. They are important too because they are made in the image of God.
Finally, we should also note that this tie of being made in the image of God allows us to share common values and to be helped and instructed by nonbelievers. J. Gresham Machen, one of the most fundamentalist Christian teachers in 20th century America said the following:
Many ties -- ties of blood, of citizenship, of ethical aims, of humanitarian endeavor-- unite us to those who have abandoned the Gospel. 
We have these ties because we are made in the image of God. The current Christian trend of insulating oneself from the world and making one's church into a gated community to keep the world out goes against the Scriptures. The let the world crash and burn if it does not repent mentality goes against valuing people because they are made in the image of God. Listening only to Christians goes against recognizing that all are made in the image of God and against the explicit words of some honorable fundamentalist Christians. If we Christians are going to make a difference in the world, then we cannot afford to treat nonbelievers as if they are from another planet.
 Let Me Stand Alone by Rachel Corrie, pg 15
 Christianity and Liberalism by J Gresham Machen, pg 44