Marriage is not man's idea, neither was it initiated by him, It was God himself who realized man's need for a companion and addressed it. To comprehend why God instituted marriage, we need to go to the bible for the answers.
Biblical reasons for marriage
*TO SOLVE THE PROBLEM OF LONELINESS
And the lord God said,it is not good that the man should be alone;I will make him an helpmeet for him.Genesis2:18
Loneliness is a complex and usually unpleasant
emotional response to isolation . Loneliness typically includes anxious feelings about a lack of connection or communication with other beings, both in the present and extending into the future. As such, loneliness can be felt even when surrounded by other people. The causes of loneliness are varied and include social, mental, emotional and physical factors.
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<center><sub>[image source](https://en.m.wikipedia.org/wiki/File:Jean_Jacques_Henner_-_Solitude.jpg)</sub></center>
*TO BE A HELPMEET
The phrase “help meet for him” translates the Hebrew words ezer kenegdo . These words are a little difficult for me to translate. Ezer literally means, “help” and is similar in meaning to the English word ‘help.’ However, kenegdo , translated ‘meet for him’, is more difficult to translate. The root word, neged , literally means ‘opposite’, ‘in the presence of’, ‘over against’, ‘in front of’, ‘corresponding to’, or ‘aside’. Literally, kenegdo means, ‘opposite as to him’ or ‘corresponding as to him’.
In Genesis 2:18 it says, "And the Lord God said, It is not good that the man should be alone; I will make him an help meet for him."
Helpmeet in my own understanding means ways the woman can help the man by prayer,sex,providing food,counsel,encouragement,comfort,by showing hospitality;by performing housekeeping duties;by helping financially,socially etc.
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<center><sub>[image source](http://s3.hubimg.com/u/256678_f248.jpg)</sub></center>
*TO AVOID FORNICATION
Now concerning the things whereof ye wrote unto me:It is good for a man not to touch a woman.Nevertheless,to avoid fornication,let every man have his own wife, and let every woman have her own husband.1corinthians7:12.
Fornication is generally consensual sexual intercourse between two people not married to each other.
In the original Greek version of the New Testament, the Greek term porneia (πορνεία) (or its variants) is used 25 times. Porneia meant prostitution, a usage still in use today.In the late 4th century, the Latin Vulgate , a Latin translation of the Greek texts, translated the term as fornicati, fornicatus, fornicata, and fornicatae. In 1611 King James Version , the first English translation of the Christian Bible used the term fornication. Other translations have used terms such as whoredom, sexual immorality (eg., Matthew 19:9 ) or simply
immorality.
*TO HAVE CHILDREN
And God blessed them and God said unto them, be fruitful,and multiply,and replenish the earth,and subdue it:and have dominion over the fish of the sea,and over the fowl of the air, and over every living thing that moveth upon the earth.Genesis1:28
When children enter into the world outside the medium of marriage,they are handicapped and often turn out to be delinquent. The absence of children does not nullify the marriage. Similarly,it is not the arrival of children that validates the marriage.