Surya let us go back in history for the concept of marriage first.

In those days if a Man had intimate relations with a Woman it was considered that both were married. In other ways sex was a sort of symbol that they were both married. But as time went on wise people decided that it might be too obscene or uncivilised if they asked established a man or wife as married after they had sex. So they decided to do a ceremony(later on each religion had their own version) where they announced both as husband and wife and then they continued their intimate relations.

Another reason that was claimed is that in those days(before civilisation came into humans mind) man did not the meaning of marriage and they just used to have intimate relations with any woman they liked and vice versa...to control this urge and what is deemed as incomprehensible later on people decided on the one man one woman concept and then announced marriage to apply this concept in reality.

Now one thing is marriage is not permanent as in it must be done for all. Marriage is a individuals own choice and they can choose if they want to share their life with another or live alone. It is just the parent's wish or hope that their children must be married that makes it seem permanent. Moreover the society having a flawed opinion of unmarried singles(more on single woman) pushed parents to make marriage permanent in their children's thoughts.

Arranged marriage was mainly created in those days to marry off a man to a woman if both are not able to find their own life partners but as times became modern it became something of a necessity to marry of a man/woman to a life partner that is deemed suitable to the parents and the society they live in. Now this concept itself is dying off soon and probably will die off once all countries become modernised.

The point of marriage is the unification of two souls who decide to share their life together. Of course primary basis will remain that if either a man or woman have intimate relations with each other they are deemed to be husband and wife unofficially but marriage is seen as a "official" announcement that both of them are husband and wife. In terms of producing the next generation, majority view the generation as proper children if their parents are married although this has been slightly shoved off in westernised countries.

As for the urge to get married it mainly rests on the individual's opinion. If they feel that they can live together without having to be married then theres no marriage. If they feel that they want to show themselves as married to the whole world then theres marriage. But basically once a man or woman live together they are married whether a ceremony is done to announce them as married or not.