The generic term "gentile" is sometimes used to refer to anyone who does not follow the Jewish faith. For Christians, the term specifically applies to those following Christianity. In the Old Testament the term "the nations" is a common expression referring to a "group" of non-Jews. In keeping with this framework, a Gentile is a person belonging to "the nations." In the early days of Christianity, only those belonging to the Jewish faith could become Christians. Therefore, once the Gentiles were also permitted to join, the division between Christianity and Judaism became increasingly apparent.
According to Christians, the first Gentile to officially convert to Christianity was the Roman Centurion Cornelius (Acts 10:1). He converted after being visited by Simon Peter, who only moments before had a vision in which he is commanded to eat animals who do not uphold kosher laws. As a Jew, he rejected the demand, saying, "Not so, Lord; for I have never eaten any thing that is common or unclean." To his surprise, the voice retorts, "What God hath cleansed, that call not thou common" (Acts: 10: 9-15), in effect foreshadowing Judaismís impending split from Christianity.
When Peter finally meets Cornelius, he talks to him about Jesus: about his teachings, his divinity, and his resurrection. After this, the Acts say, "the Holy Ghost fell on all them which heard the word" (Acts 10: 45), and the Jews in attendance were quite astonished at Corneliusí ability to "speak in tongues" (a term used in the New Testament to refer to the language given to the followers of Christ).
Seeing this, Peter orders the baptism of Cornelius, marking his conversion, "Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we?" (Acts 10: 47).
The Council of Jerusalem
What was so controversial about this was that Gentiles were not Jewish, and more specifically, not circumcised, which some Jewish Christians held was necessary before conversion could take place. To resolve this issue, the Council of Jerusalem was convened in 50 B.C.E.
The followers of Simon Peter and James the Just maintained that observance of certain Jewish rituals - and in particular, circumcism, should be a necessary prequisite tp Christian conversion. This statement, made by James, is referred to as "The Apostolic Decree":
Wherefore my sentence is, that we trouble not them, which from among the Gentiles are turned to God: But that we write unto them, that they abstain from pollutions of idols, and [from] fornication, and [from] things strangled, and [from] blood. For Moses of old time hath in every city them that preach him, being read in the synagogues every sabbath day. (Acts 15:19-21)
On the other side of the debate were followers of Paul, who disputed such claims, saying that it was hypocriticial to force the Gentiles to live as Jews, when many Jews - such as Simon Peter himself - live like Gentiles themselves.
The council ruled in favor of Paul, stating that Gentile conversions need not necessitate circumcision, thus serving to further distinguish the two religions.