there is no purpose but it has alot of benifits. I know my marriage will probably end in divorce but i would get married because its tradition

I think nowadays many people still participate in marriage in our society b/c we still hold on to the same religious and social beliefs of our parents. While we are technologically advanced, we are not as evolved sociologically.
According to sociologists, those who are married are actually happier and live longer than their single counterparts (in the long run, not day-to-day)
And antropologists claim that marriage provides exclusive *** with your partner.
So while we are an individualistic and independent-minded socieity, our psychological need to be with others still needs to be fulfilled. And even though financially we can be independent, some of us are still competing with the Joneses and in order to do that, you need a 2-family income.

Hi Ilya

What is the purpose for whom?

Regardless of what the State, the Church or anyone else says, each couple has their personal reason for wanting to get, or not get, married.

Therefore there is no meaningful or useful single answer to your question.