In writing the Bible, Moses and the various disciples of Jesus viewed marriage as an exclusive and sacred union between one man and one woman. In fact this sacred view is found in some of the very first words of the Bible.
Genesis 1:27 says, “So God created man in His own image, in the image of God He created him; male and female He created them.” Genesis 2:23-25 adds, “The man said, ‘This is now bone of my bones and flesh of my flesh; she shall be called ‘woman,’ for she was taken out of man.’ For this reason a man will leave his father and mother and be united to his wife, and they will become one flesh.
This “one flesh” union is the merger (or actually the re-merger) of two different but similar constituent parts (one male and one female) united physically, mentally and spiritually via a life-long marital covenant. Jesus said the husband and wife “are no longer two, but one,” and He added, “What God has joined together, let man not separate” (Matt 19:6).
Two men united in “marriage” remain two men, and two women united in “marriage” remain two women. However, a husband and wife united in marriage creates something new: a “one flesh” union. This marital oneness reflects the oneness of God, and as the oneness of God creates new life, marital oneness has the potential to create new life via children (new men and women).
Putting aside the issue of those who are attracted to others of the same sex, same sex “marriage” is clearly not sanctioned by God.