Therefore, as we have opportunity, let us do good to all people, especially to those who belong to the family of believers (Galatians 6:10). 

A number of people have asked me about this because they come across verses that carry the expression "one another." For example, Christians are commanded to "love one another." Does this mean that Christians are to love other Christians to the exclusion of non-Christians? Simply put, no. However, as the verse above and others suggest, Christians ought to share a deeper love with other Christians. 

Doesn't this make sense? Becoming a Christian also means becoming a child of God, being a member of the Body of Christ, entering the family of God. Therefore, just as we might show particular affection for our own family members, we ought to show a similar preference of affection for our brothers and sisters in Christ. 

In fact, our relationship with our Christian siblings should be deeper and stronger than even our biological ties. For while our biological ties will end in this lfe, our spiritual ties endure forever. Even when Jesus' mother and brother sought his attention, Jesus said, 

My mother and brothers are those who hear God’s word and put it into practice (Luke 8:21).

Now, again, this does not mean that Christians ought not to love non-believers. Certainly, when Jesus taught believers to love their enemies, He had non-believers in view:

“You have heard that it was said, ‘Love your neighbor and hate your enemy.’ But I tell you, love your enemies and pray for those who persecute you, that you may be children of your Father in heaven. He causes his sun to rise on the evil and the good, and sends rain on the righteous and the unrighteous. If you love those who love you, what reward will you get? Are not even the tax collectors doing that? And if you greet only your own people, what are you doing more than others? Do not even pagans do that? Be perfect, therefore, as your heavenly Father is perfect (Matthew 5:43-47).

When Jesus taught the Parable of the Good Samaritan, He showed that neighborly love must not be exclusive (Luke 10:25-37).

What is more, how can we be a witness to others if we do not share the love of Christ with them? Even before there were any Christians, Christ loved the unbelievers who would later come to faith. In other words, He loved them while they were still in their sinful, unbelieving rebellion against God: 

You see, at just the right time, when we were still powerless, Christ died for the ungodly. Very rarely will anyone die for a righteous person, though for a good person someone might possibly dare to die. But God demonstrates his own love for us in this: While we were still sinners, Christ died for us (Romans 5:6-8).

Now, while the Scripture teaches that we ought to have a particular love for fellow believers, we should also understand that the converse is true too, namely, that we should have a stricter judgment of one another in view of the high standards we share:

What business is it of mine to judge those outside the church? Are you not to judge those inside? God will judge those outside. “Expel the wicked person from among you" (1 Corinthians 5:13-14).

For it is time for judgment to begin with God’s household (1 Peter 4:17).

“If your brother or sister sins, go and point out their fault, just between the two of you. If they listen to you, you have won them over. But if they will not listen, take one or two others along, so that ‘every matter may be established by the testimony of two or three witnesses.’ If they still refuse to listen, tell it to the church; and if they refuse to listen even to the church, treat them as you would a pagan or a tax collector (Matthew 18:15-17).