Marriage can only exist between one man and one woman because this is how God, as Creator of mankind and of marriage, intended it. Genesis 1:27 speaks to the overview of God creating man and woman. “So God created man in His own image; in the image of God He created him; male and female He created them.” Then in Genesis 2, we see a micro-view of God creating man and woman individually. In verse 7 of chapter 2, God creates a man, Adam. Then in verses 21-22, we see God create a woman. The first time Adam sees her, Scripture tells us his reaction and gives us a picture of what marriage is supposed to be. “And Adam said, ‘This is now bone of my bones and flesh of my flesh; she shall be called Woman, because she was taken out of man.’ Therefore a man (one man) shall leave his father and mother and be joined to his wife (one woman), and they shall become one flesh” (Genesis 2:23-24). One man for one woman for all time. Jesus spoke to this in the Gospel of Matthew, affirming God’s design by quoting some of what we just read from Genesis.
“And He answered and said to them, ‘Have you not read that He who made them in the beginning made them male and female, and said, ‘For this reason shall a man leave his father and mother and be joined to his wife, and the two shall become one flesh?’ So then, they are no longer two but one flesh. Therefore what God has joined together, let not man separate” (Matthew 19:4-6).
It is clear from these verses that God created one man for one woman and that He intended them to be joined together in a lifetime commitment. No longer bound to their parents, now only bound together as man and wife; a man and a woman become one flesh. Any other type of union is NOT marriage by God’s definition, and since He is the one who created marriage, His is the only definition that matters.