Christian, as an adjective, means "relating to or professing Christianity." As a noun, it means "a person who follows the teachings of Christ." The word comes from the Greek Christus, meaning "Christ" or "Messiah", and anum, meaning "of" or "pertaining to." In the first century, because Jesus was Jewish and most of His followers were Jewish, Christianity was first seen as a new sect of Judaism. So the term Christian could be better understood as "those of the Messianic party" in this early context. The Greeks gave these types of names to those who sided together behind political leaders. For example, they termed those who were loyal to General Pompey as "Pompeians" and those who excessively praised Nero Augustus as "Augustinians." So "Christian" was the term for those who believed Jesus was the Jewish Messiah or Christ.
Generally, the Romans did not grant religious freedom to the peoples they conquered. Instead, Rome simply added new gods to their pantheon and required conquered peoples to worship their gods along with all the others in Roman temples. However, Jews were given special permission to continue their monotheistic religious practices. So it was advantageous for early Christians to identify as a new Jewish sect. Conversely, as the Jews began to rebel against Roman rule and the Romans became increasingly hostile toward the Jews, followers of Jesus saw the need to differentiate themselves from the Jewish faith. By the time Rome destroyed the temple in Jerusalem in AD 70, followers of Jesus were using the term Christian for themselves. Despite this distinction, Christians still suffered considerable persecution periodically until the rule of Constantine and the Edict of Milan in AD 313.
Since that time, the term Christian has meant different things to different people. Although some people refer to a Christian as someone who believes in God but is not Jewish or Muslim, or someone who simply professes to be Christian perhaps for a cultural reason, a true Christian is someone who follows Jesus Christ in faith and obedience, acknowledging Him as Lord and Savior. A true Christian is not merely defined by religious affiliation or cultural identity but by a transformed heart, evidenced by love for God, faith in His Word, and a life that reflects Christ’s teachings. As Jesus said, “If you love me, you will keep my commandments” (John 14:15). The defining mark of a Christian is not just belief in Christ but a commitment to live in accordance with His will, trusting in His grace for salvation and seeking to glorify God in all things.