Genesis 2:24 New International Version (NIV)
24 That is why a man leaves his father and mother and is united to his wife, and they become one flesh.
Marriage was given by God as a gift to Adam and Eve. They were created perfect for each other. Marriage is not a convenience or from a particular culture, it was initiated by God. The man leaves his parents. He promises himself to a wife. The man and woman are joined together. They take care of each others welfare, the love each other above all others, and are united in commitment were there is only intimacy between the two in the covenant of the marriage. All strong marriages include these traits that originated from God.