Baptism is the rite that God uses to specify that a person has become a part of the body of Christ — the church. After the election of the President of the United States, the winner, by law, is not the President until he takes the oath of office. That doesn’t fit too well when a President is incumbent and wins, but if he’s newly elected, then he is not President. The previous president is still the president until he takes the oath of office. Similarly, baptism signifies membership in the body of Christ, the church.