Antioch

Antioch was one of the most cultural and ethnic diverse cities of its days. In Antioch there were walls that separated the different groups from one another. There was the Syrian section, the Jewish section, the African section and the Greek section. Then along came some believers. "Now those who had been scattered by the persecution that broke out when Stephen was killed traveled as far as Phoenicia, Cyprus and Antioch, spreading the word only among Jews. Some of them, however, men from Cyprus and Cyrene, went to Antioch and began to speak to Greeks also, telling them the good news about the Lord Jesus. The Lord’s hand was with them, and a great number of people believed and turned to the Lord." Acts 11:19 - 21
What was happening here? People were coming to Christ across the walls and that is why they called them Christians. They had no other name to call them but ones like Christ. The people had never seen anything like this before. When the church was in Jerusalem made up of only Jews it was thought to be a Jewish sect but now there were Syrians, Greeks, Jews, Africans and more coming to Christ. The church was no longer for the rich or the male or the Jew, it was for everyone.
That is why love is the characteristic of a Christian. It is the unique teaching of the person of Jesus that explains this. Christianity brought down all the barriers because of a unique truth that Christ was the Son of God. People may not have agreed with that truth but when they saw the love that brought down the walls then they had to take a second look and ask, "Maybe He is the Son of God."