What Identifies A True Christian?

Jesus Christ And His Deciples Did Not Use Carnal Warfare

Jesus Christ, "the exact reflection of God," conquered the world with his faith. In his weakness of allowing and submitting to wickedness, he bought mankind back to God with his perfect blood. "For the son of man came as a ransom in exchange for many." As "ambassadors of Christ," can true Christians be killing one another and still be loving on another? Are there any exceptions? (Matt 20:28)