Marriage is a life long commitment to me. It means sticking with my best friend, even when we have serious disagreements. It means taking care of your mate through good AND bad times. It means knowing you have someone to grow old with. My wife & I just had our 41st anniversary two days ago.
Marriage doesn't mean a whole lot really. It's mostly for the people surrounding the couple, parents and family, who want to live together. That and benefits provided from citizenship or employment, estate settlement, and decisions made in the event of incapacity. Other meanings for marriage are religious compliance and ones own security as false as that may be. People surrounding the couple apply pressure to "tie the knot" for many reasons so entering a marriage satisfies these people. Governments and employers want that civil ceremony connecting the couple which helps organize tax rolls, insurances, benefits, inheritance, and relationship status. There are times when one cannot make decisions medically and if there is a marriage it is a given that the partner can do so, usually no questions asked. They don't even ask for proof of marriage. Just say so is good enough. Then religion plays a part in many marriages. so does security. Security in that by saying "I DO" the partner feels that they will not be abandoned. It's kinda silly thinking since, as someone else already wrote, marriage is the chief cause of divorce.
The hopeless romantic in me, says marriage means you really love someone and want to work really hard to try and make it work. The cynical bitter realist in me, says that it's just another relationship that will end up hurting you either by ending it, or someone dying, and a financial/legal hassle. So why bother? Don't need to pay people to declare your in love or hate.