Pope Francis pulls out an insight from another national conference, that of France, to suggest that marriage is more than just the emotional commitment of two people:
66. The family is experiencing a profound cultural crisis, as are all communities and social bonds. In the case of the family, the weakening of these bonds is particularly serious because the family is the fundamental cell of society, where we learn to live with others despite our differences and to belong to one another; it is also the place where parents pass on the faith to their children. Marriage now tends to be viewed as a form of mere emotional satisfaction that can be constructed in any way or modified at will. But the indispensible contribution of marriage to society transcends the feelings and momentary needs of the couple. As the French bishops have taught, it is not born “of loving sentiment, ephemeral by definition, but from the depth of the obligation assumed by the spouses who accept to enter a total communion of life”.[CONFÉRENCE DES ÉVÊQUES DE FRANCE, Conseil Famille et Société, Élargir le mariage aux personnes de même sexe? Ouvrons le débat! (28 September 2012)]
Evangelii Gaudium suggests two social purposes.
- Where people learn to be social beings despite differences
- Where people learn to belong to one another
And for Christians (plus, presumably people of other faiths as well) there is the element of passing belief to a new generation.
Catholic Sensibility 
Reblogged this on Mark baird's Blog and commented:
true
Very true.