The word 'reasons' admits of two meanings:
1) What caused something to happen, what triggered it, etc.
2) What the something accomplishes in the world.

Thus, if I say 'My wife went to the store because we are out of apples'; no one (who understands women) is surprised when she comes home with a car full of groceries. The missing apples were the 'trigger' for my wifes decision to go to the store. However going to the store fulfills many functions, including the purchase of cheese, bread, milk etc.

The page 'When need so requires' lays out what we see as the fundamental 'causitive' factor in a good marriage: the spectre of fornication, and the contrary joy of sexual fulfillment in marriage. However there are other things that Scripture tells us that marriage accomplishes, such as:

1) Companionship: 'It is not good' we are told, for Adam to be alone.
2) Dominion: Adam was given a task, and Eve as a helpmeet to fulfill it.
3) A Godly Seed: the wife of the youth will, if fruitful, produce a seed which the couple can train up in Godliness.
4) A blessing on the man: 'she will do him good and not evil', 'he who finds a wife has found a good thing'.


Going through the passage in Genesis, what do we see as the original purpose(s) of marriage?

From Gods perspective we have:
1) A statement of need/deficit: ‘It is not good that the man should be alone’.
2) A statement of intention/reaction: ‘I will make a help meet for him’.
3) A statement of action/response: ‘21And the LORD God caused a deep sleep to fall upon Adam, and he slept: and he took one of his ribs, and closed up the flesh instead thereof; 22And the rib, which the LORD God had taken from man, made he a woman, and brought her unto the man.’ (Note: God performed some actions in conjunction with this that may well be part of the process. I have written only the ‘core’ here.)

From Adams perspective we have:
1) A perspective of need: ‘19And out of the ground the LORD God formed every beast of the field, and every fowl of the air; and brought them unto Adam to see what he would call them: and whatsoever Adam called every living creature, that was the name thereof. 20And Adam gave names to all cattle, and to the fowl of the air, and to every beast of the field; but for Adam there was not found an help meet for him.’
2) The reception of an action:T ‘21And the LORD God caused a deep sleep to fall upon Adam, and he slept:: and he took one of his ribs, and closed up the flesh instead thereof; 22And the rib, which the LORD God had taken from man, made he a woman, and brought her unto the man.’
3) His response to Gods action: ‘23And 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. 24Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh.’

And then the reaction of the couple was: ‘25And they were both naked, the man and his wife, and were not ashamed.’