God's rules regarding marriage are not arbitrary. Everything in human marriage is to be, Ephesians 5:25, 'with reference to Christ and the church.' That's why within marriage there are male and female roles - whereby the husband shows Christ and the wife shows the church. That's why God forbids divorce - because Jesus would never leave us nor would we desire to leave Him. That's why sex before marriage is wrong - because the joining of us and Christ only happened after a covenant was made. That's why marriage in God's economy is between one man and one woman - because Jesus didn't marry Himself nor did the church marry herself. That's why married children leave their parents to form a new union - because the union with Christ is to be dominating over all other relationships. That's why within marriage couples now become one flesh - because we are in Christ and He is in us. That's why adultery is wrong - because God would never cheat on us nor should we spiritually cheat on Him by running after other gods.