When I was in high school last century, the sister we had for religion tried to teach us about marriage.  She said the purpose of marriage is for procreation and for the mutual benefit of the husband and wife.  She asked us what that meant.  Our class understood the concept of procreation and we agreed the mutual benefit...was because when old widows & widowers got married they were not going to procreate but needed a partner to go to cocktail parties, community events and travel with.  A classmate told sister that these "old people, over 35" certainly would not do it.  Sister, who was about 23  agreed with  the importance of companionship in marriage and made no comment on our other observation.