A Christian is someone whom God has united to His Son, Jesus Christ.
God gives him new life spiritually (he is “born again”) so that he recognizes his rebellion (“sin”) against God and desires to turn from his sin and be right with God:
God enables him to trust in Jesus Christ who has died to take the punishment for his sins and offers the credit of Christ’s perfect obedience to the account of anyone who believes in Him.
God gives him the Holy Spirit to enable him to work towards his new desire to become more and more like Jesus (to be holy) and follow Jesus as God’s servant.
A Christian is a person whose greatest joy is to know and honour God in this world and who looks forward to pleasures for evermore in Christ in a newly consummated creation.