Paul wrote a passage of Scripture to a group of Christians he had never met, we call it the book of Romans. In this book he wrote a chapter explaining how Christians act, specifically toward one another and to the world. He told them that they were to show themselves as a sacrifice for the Lord (Rom. 12:1). He told them that Christians are all one in the body of Christ, the church (Rom. 12:5, cf. Eph. 1:22-23). That they were to love without hypocrisy and be loving toward one another as brothers (Rom. 12:9-10). And, that they were to help those in need, pray for those who treated them bad, and important to this topic, rejoice with those who are rejoicing and weep with those who are weeping (Rom. 12:13-15).
Christians look at this world in a different light than those outside of the church. We look at it and know that there is always going to be someone in need of our prayers, that there will always be someone who needs our encouragement or that is having a wonderful time in life and needs us to be happy with them. Through all of the good times and bad, Christians are the people that have the ability and obligation to be there for everyone that needs it. So, as we see Facebook statuses or see people out and about, we should always remember that just showing someone that we care may make the difference in their day and their eternity.